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Death Investigation Systems: Decomposition, Patterns, and Rates
Death Investigation Systems: Decomposition, Patterns, and Rates MK Marks and MA Tersigni-Tarrant, University of Tennessee, Knoxville, TN, USA r 2016 Elsevier Ltd. All rights reserved. This article is reproduced from the previous edition, volume 2, pp 148–152, © 2005, Elsevier Ltd.
Abstract Decomposition is the process by which organic substances are broken down into a much simpler form of matter. This chapter describes decomposition rates and stages, and a description of time since death estimation.
Introduction Forensic pathologists spend the majority of their careers examining the fresh, or recently expired, decedent rendering expert opinion on cause and manner of death, identity, and time since death (TSD). Estimations of TSD in the recently deceased follow a traditional, time-honored understanding of algor, livor, and rigor mortis that substantiate a ‘ballpark,’ but legally defensible, estimation for the legal community they serve. Exposure to bodies subjected to extended postmortem time prior to discovery comes from years of practical experience appropriate for understanding those events even more vague than the highly variable mortis occurrences. In fact, most expertise in understanding the postmortem processes of human soft-tissue decomposition is primarily acquired by rare case-based examples, reinforced by similar cases, unfortunately, sometimes only through memory long after the remains have left the facility. Pathologists venture estimations of TSD into the bloat stage of decomposition and even after perforation of the thoracoabdominal wall. However, once viscera and tissues have liquefied or desiccated, they become hard-pressed to discern any meaningful histological evidence or pathological processes and are unable to rule on cause of death. Keeping in mind that temperature primarily guides the postmortem decomposition process, most routine forensic pathological protocol can become abbreviated in as little as 1 week after death. At the other extreme of postmortem time, the biological anthropologist traditionally examines museum collections of prehistoric and historic skeletons that are long devoid of the moist soft-tissue envelope so important to forensic pathology. Their examination involves the odontoskeletal system only and, while they may be able to venture a manner of death, provided there are perimortem traumatic signatures, little else is possible. This is not to imply that pathologists are not astute in the examination of bone or that anthropologists know nothing about soft tissue. By virtue of the research facility, forensic anthropology is now developing a legally defensible battery of expertise to collaborate with
8
forensic pathologists in understanding the complex processes between fresh remains and skeletal remains.
Anthropological Research Facility There has been remarkable progress in our understanding of the complexities of the later postmortem process of soft-tissue decomposition since the late 1970s. Much of this knowledge stems not only from the burgeoning development of forensic anthropology as a discipline within the American Academy of Forensic Sciences and a resource for forensic pathological inquiry, but from the formation and maintenance of an outdoor research facility at the University of Tennessee, USA, where these processes of human soft-tissue decomposition have been studied. William M. Bass envisioned firsthand witnessing of these processes in a natural setting with bodies donated to scientific research. Presently, 600 donations have been received at the research facility. The facility is a wooded 4-acre tract protected by a chain link fence with razor wire and a privacy fence and under constant surveillance. While carnivores are inhibited from inside access, rodents often gain access. The facility provides the unique opportunity to study longitudinally the accumulated effects of decomposition of soft tissues under a wide range of variables, including temperature and humidity, clothing, burial, water submersion, effects of sun exposure, and body posture/ gravity. Also examined are biochemical soil change, odor, and burial/grave testing using ground-penetrating radar technology. Finally, the lion’s share of forensic entomology is derived from facility research. Most of this research has been fueled by collaboration with law enforcement and our attempts to stage research that answers specific problems relating to TSD. This natural laboratory holds a colossal advantage over the cross-sectional exposure provided by isolated decomposition cases introduced to the forensic pathologist. No matter how accurate the assessment of postmortem time may be, after identification the remains are removed for burial/cremation without any
Encyclopedia of Forensic and Legal Medicine, Volume 2
doi:10.1016/B978-0-12-800034-2.00135-X
Death Investigation Systems: Decomposition, Patterns, and Rates
opportunity to study the progression of the events. So, the pathologist gains expertise in soft-tissue decomposition after a career of exposure gaining confidence for testimony. No one doubts the TSD testimony afforded by the senior forensic pathologist armed with a career of cases. However, the resident or new pathologist has little recourse as a result of limited exposure to decomposed bodies and therefore is poorly equipped to render expert opinion. The facility allows examination and appreciation of decomposition daily, weekly, monthly, and even, annually. In a sense, the research facility is one giant validation study. Besides a laboratory to study decomposition, the research facility provides an outdoor classroom for training graduate students in forensic anthropology. The bulk of the research conducted has been formulated through their interests as associated with particular crime-scene events. Also, local, regional, state, and national law enforcement agencies, members of the medicolegal community into whose service the forensic anthropologist is called, as well as canine search and rescue teams, are afforded the training opportunity in clandestine grave discovery and excavation techniques at the research facility. The anthropological research facility contributes to forensic science by enumerating the changes that occur during decomposition of human remains related to temperature and other previously described variables. Through this type of longitudinal study, researchers have determined the sequence of stages through which human remains move to reach the skeletal state. Some of these stages are better correlated with TSD than others, but nonetheless, each body, if allowed to decompose naturally, will eventually undergo each of the following stages.
reticulum by adenosine triphosphate (ATP), but with little or no ATP production at death, increased calcium causes muscle contraction. Rigor starts 2–6 h after death, typically manifested by stiffness in the jaw and neck, and then spreading to the rest of the body over the next 4–6 h and lasting from 24 to 18 h after onset. These temporal estimates are just that, estimates, and pathologists have long recognized situations of delayed onset or abbreviated duration based primarily upon temperature. Similarly, temperature controls the onset, tempo, and duration of the remaining postmortem processes of decomposition. One of the externally visible signs of autolysis is skin slippage. During autolysis, the junction of the epidermis and dermis is weakened by the release of hydrolytic enzymes. This loosening allows the epidermal layer to slip off the dermal layer, giving rise to the term skin slippage (Figure 1). The products liberated by autolysis fuel the next process of decomposition: putrefaction. Putrefaction is the consumption of soft tissues through the exponential proliferation of endogenous enteric bacteria. It is caused by release of acidic autolyzed cellular contents that, along with an almost completely anaerobic environment, creates a perfect environment for bacterial proliferation. This first occurs in the cecum where the largest population of endogenous bacteria is found (Figure 2). Hydrogen sulfide (H2S) gas is a byproduct of this bacterial growth from the interaction with the iron in hemoglobin to form a black precipitate, ferrous sulfide (FeS). This darkening is the agent that discolors the body’s circulatory architecture as intravascular hemolysis/marbling (Figure 3). Initially, other cecal discoloration is caused by the hydrolytic enzymes attacking the biliary system to release biliverdin, bilirubin, and urobilin pigments into the
Stages of Decomposition The biochemical process of internal decomposition begins immediately at clinical death with a process called autolysis. Autolysis is the irreversible cascade of cell death that destroys structural integrity and the cell-tocell junction. Besides leading to widespread tissue necrosis, autolysis triggers three events that produce the three familiar externally visible manifestations: algor, livor, and rigor mortis. Algor mortis is internal cooling of the body to ambient temperature. Livor mortis is the gravitational pooling of blood in the capillary beds of dependent body parts. Initially, livor mortis is ‘unfixed’ and gentle pressure on a livor area will blanch. After 8– 12 h, livor becomes ‘fixed’ as capillary blood begins clotting. Rigor mortis is stiffening of muscles fibers after death, resulting from the flood of calcium ions into the sarcomere (contractile units of the muscle fiber). During life, this calcium is pushed back into the sarcoplasmic
9
Figure 1 Skin slippage on the plantar portion of the foot associated with early decomposition. This phenomenon occurs due to the weakening of the junction between the dermis and epidermis during decomposition, causing the epidermis to slip away from the dermis.
10
Death Investigation Systems: Decomposition, Patterns, and Rates
Figure 2 Purplish-green discoloration in the cecal region of the lower right abdominal quadrant associated with early decomposition caused by the proliferation of endogenous bacteria producing hydrogen sulfide in a nowanerobic environment.
Figure 3 The marbling pattern (intravascular hemolysis) of the circulatory system that appears in early decomposition, caused by the invasion of the circulatory system by hydrogen sulfide gas, producing bacteria. This same process of gas production results in the bloating that is characteristic of the middle stages of decomposition.
abdominal tissues. The bloating stage results from the release of vast amounts of hydrogen sulfide within the body’s organs and cavities from bacterial growth in the anaerobic environment. This gas diffuses with ease through body tissue due to its small molecular structure. Gas accumulation within the body causes distension of the abdomen and swelling of limbs and facial structures (Figure 4).
Insect Activity It is during the bloat phase that insects become a major factor in the modification of tissues. Forensic
Figure 4 An adult male in full bloat 2 weeks postmortem during late spring. Note the extreme expansion of the abdominal cavity causing splitting of the soft tissue of the lateral chest wall. Also note the elevated posture of the pelvic limbs.
entomologists learned that insect growth, feeding, and migration are generally genus-specific and are as driven by temperature, daily and seasonally, as the events of internal biochemical decomposition. Sarcophagic insects and their activity are the litmus test for soft-tissue reactions during decomposition. Insect interest in a dead body is instantaneous upon placement at the Anthropological Research Facility. Blowflies are usually first to arrive, ovipositing in any natural or traumatically created shaded orifice. These include the ears, nostrils, mouth, eyes, hair, and the shaded regions of the genital region and the ground – body interface. At the crime scene, detection of differential decomposition of soft tissues and insect activity in areas other than these regions signals peri- or postmortem trauma that has provided an artificial segue for ovipositing (and subsequent feeding). It is important to realize that, while numerous arthropods habituate the host off and on during the entire decomposition tenure, blowfly larvae (maggots) are responsible for ingesting 95% of the body mass. After eggs hatch, larvae develop through three distinct stages of growth that are termed instars. After the final stage, third-instar maggots migrate away from the body, seeking a dark, cool, subterranean location (or clothing) to generate a pupal casing where they remain until emerging as adult blowflies. The entomologist, using a strategy of collecting a representative sample of maggot sizes on the body to capture growth variation, and looking away from the body for pupal casings, can estimate with confidence the length of time the body has been colonized and thus narrow a postmortem interval. At the beginning of the drying phase, other arthropod species become more interested in the tissues and sites of fluid runoff. These include, but are not exclusive to, dermestid beetles, ants,
Death Investigation Systems: Decomposition, Patterns, and Rates
wasps, and other types of beetle that continue to ingest the drying skin and remaining cartilaginous regions. By determining species, one can identify the most reliable postmortem interval, as some species, for example, will not colonize when the remains are too moist or too dry. As bloat subsides, deflation of the abdomen occurs, with drying of the skin. Drying begins at exposed tissue margins, that is, lips, nose, eyelids, and wounds, besides hands and feet. Generally, on the level of the entire body, drying follows bloat, but specific regions dry more quickly (tissue margins) than the rest of the body. The drying stage refers to the drying of the entire body or large portions of it, not these focal areas. Coincident with drying is rib head and cervical bone exposure. It is not uncommon for the stages of bloat and drying to coincide. If the soft tissues (including skin) have not been destroyed or decomposed by bacteria or arthropods, there are two avenues in which decomposition can proceed in order to reach a skeletonized state: adipocere formation and/or mummification. Adipocere is a white or cream-colored waxy, homogeneous substance derived from body fat that may form during the decomposition of remains in a moist environment, that is, water submersion, damp grave. The chemical process is termed saponification and used interchangeably with adipocere formation. Adipocere formation appears to benefit from a catalyst of alkaline, such as formaldehyde, which is commonly used in embalming fluid. Yet, certain soils are highly alkaline, which also contributes to adipocere formation. Alkaline will hydrolyze the fat, turning it into this soap-like substance. Mummification is the drying of soft tissues to take on a hard, leathery appearance. This is most common in arid areas with low humidity or little precipitation. However, it is the terminal stage in soft-tissue decomposition processes at the anthropological research facility, even though mummification happens more quickly in dry arid environments. The speed with which moisture and fluids evacuate the body is much quicker in an arid environment, though no time estimates can be given due to lack of a research facility in that climate. Complete mummification often occurs in individuals with little body fat since fat can have enough moisture content to prevent complete mummification (Figure 5).
Estimation of Time Since Death Accumulated degree days (ADD) are defined as the total number of degrees accumulated in a given time period, represented by the highest temperature for each period. Thus, the ADD for a week is the highest temperature for each day, added to that of the following day. So, if the temperature is 20 1C each day, the ADD for the week is 140 1C (7 20 ¼ 140). Vass used this measure to track the degree of decomposition, thereby linking
11
Figure 5 An adult male in mummified stage of decomposition (2 months after death) prior to skeletonization.
temperature with time. Essentially, if a body was in x state of decomposition, based on the chemical breakdown of certain lipids, Vass could backtrack the length of time the body had been exposed by adding up the temperatures for the preceding days and comparing that to actualistic studies performed at the facility. This provided a standard for chemical values versus the ADD to be set. This standard would be compared to the chemical values found at a crime scene and the corresponding ADD value could be used to determine the length of TSD. With the ADD value, the TSD estimate is calculated by removing the temperatures from the preceding days until this equals 0. This would give an estimate of the number of days the body had been decomposing in that area. Marks and colleagues used ADD but compared them to stages of decomposition. The ADD was not consistent across decomposition stages and the researchers were hard-pressed to get narrowed ADD estimates to fall within single decomposition stages for everybody. Instead, there was an overlap of overlap upon different stages of decomposition. The problem may be that ADD is not representative of the ‘amount’ of accumulated temperature and does not take into account the 24-h temperature fluctuations. Vass also recognized this and attempted to correct it by adjusting ADD to cumulative degree hours (CDH). This measure represents an average value of each 12-h period (the high þ the low/2). Thus, if temperature is 10 1C at 12 p.m. and 0 1C at 12 a.m., the CDH would be 5. For one day, there are two calculations of CDH (one for each 12-h period). We have found that this procedure does not adequately characterize the temperature fluctuations in a 24-h period either, and, if a body decomposition scene is not covered by a temperature gauge, then it is virtually unusable. These problems are currently being resolved through ongoing facility experimentation.
12
Death Investigation Systems: Decomposition, Patterns, and Rates
Figure 6 A woman in differential decomposition. Note the advanced state of decomposition of the head, which has been completely blackened, while the rest of the body retains a near-natural skin color.
This plethora of research in determining TSD implies that there are many circumstances and variables that affect postmortem interval estimation. It is by no means an exact science but rather an approximation. One major result of this longitudinal study affords the researcher the luxury of seeing commonality between the decomposition processes of each body and more importantly, the ability to discern where the normal process of decomposition has been compromised or altered. Nowhere is this more applicable than in forensic cases that display differential decomposition. Differential decomposition is the term used to describe a situation where one body exhibits different stages of decomposition in different parts of the body. It is paramount for a forensic anthropologist to determine what caused this differentiation. For example, Figure 6 depicts a forensic case where the body of a woman was found in a wooded area. It is clear that her head is in a more advanced state of decomposition than the rest of her body. The goal is to determine why the head has moved more quickly through the decomposition phases, or perhaps, why the decomposition of the rest of the body has been retarded.
Conclusion We realize that the process of decomposition is regionally variable: temperatures and humidity that guide decomposition in the southeast will probably not apply to other regions of the USA. However, all bodies will go through the same itemized changes. Decomposition will
not skip stages, but the specific chronology of change will vary slightly from victim to victim based on other variables. It is important to realize that, regardless of location in postmortem time, decipherment of human decomposition will never be an exact science. Like growth and development, decomposition is biological continuum that cannot be easily quantified and qualified. Hence, understanding the deterioration of multiple criteria is necessary to best satisfy our curiosity. The anthropological research facility provides a unique opportunity to understand the processes of human soft-tissue decomposition and the research agenda is partially fueled by collaboration and consultation within the medicolegal community. The research potential of the facility, not unlike a crime scene, provides a crossroads where the perspectives of many forensic investigators intersect and flourish.
See also: Anthropology: Morphological Age Estimation. Anthropology: Sex Determination. Entomology. Postmortem Changes: Overview
Further Reading Bass, W.M., Jefferson, J., 2003. Death’s Acre: Inside the Legendary Forensic Lab the Body Farm Where the Dead Do Tell Tales. New York, NY: G.P. Putnam’s Sons. Byrd, J.H., Castner, J.L. (Eds.), 2001. Forensic Entomology − The Utility of Arthropods in Legal Investigations. Boca Raton, FL: CRC Press. Catts, E.P., Haskell, N.H., 1990. Entomology and Death − A Procedural Guide. Clemson, SC: Joyce’s Print Shop. Love, J.C., 2001. Evaluation of decay odor as a time since death indicator. Thesis, University of Tennessee, Hodges Library/Thesis/Dissertation. Love, J.C., Marks, M.K., 2003. Taphonomy and time: Estimating the postmortem interval. In: Steadman, D.E. (Ed.), Hard Evidence: Case Studies in Physical Anthropology. Upper Saddle River, NJ: Prentice-Hall, pp. 160–175. Marks, M.K., Love, J.C., Elkins, S.K., 2000. Time since death: A practical guide to physical postmortem events. American Journal of Forensic Science Proceedings, 181–182. Miller, M.L., 2002. Coupling ground penetrating radar applications with continually changing decomposing human targets: An effort to enhance search strategies of buried human remains. Thesis, University of Tennessee. Hodges Library/ Electronic Thesis. Miller R.A., 2002. The affects of clothing on human decomposition: Implications for estimating time since death. Thesis, University of Tennessee. Hodges Library/ Thesis/Dissertation. O’Brien, T.G., 1995. Human soft-tissue decomposition in an aquatic environment and its transformation into adipocere. In: Proceedings of the 47th Annual Meeting of the American Academy of Forensic Sciences, 13-18 February, pp. 155−156. Seattle, WA; Colorado Springs, CO: American Academy of Forensic Sciences. Srnka, C.F., 2003. The effects of sun and shade on the early stages of human decomposition. Thesis, University of Tennessee. Hodges Library/Thesis/ Dissertation. Vass, A.A., 1992. Time since death determinations of human cadavers utilizing soil solution. Thesis, University of Tennessee. Hodges Library/Thesis.
Abstract Decomposition is the process by which organic substances are broken down into a much simpler form of matter. This chapter describes decomposition rates and stages, and a description of time since death estimation.
Introduction Forensic pathologists spend the majority of their careers examining the fresh, or recently expired, decedent rendering expert opinion on cause and manner of death, identity, and time since death (TSD). Estimations of TSD in the recently deceased follow a traditional, time-honored understanding of algor, livor, and rigor mortis that substantiate a ‘ballpark,’ but legally defensible, estimation for the legal community they serve. Exposure to bodies subjected to extended postmortem time prior to discovery comes from years of practical experience appropriate for understanding those events even more vague than the highly variable mortis occurrences. In fact, most expertise in understanding the postmortem processes of human soft-tissue decomposition is primarily acquired by rare case-based examples, reinforced by similar cases, unfortunately, sometimes only through memory long after the remains have left the facility. Pathologists venture estimations of TSD into the bloat stage of decomposition and even after perforation of the thoracoabdominal wall. However, once viscera and tissues have liquefied or desiccated, they become hard-pressed to discern any meaningful histological evidence or pathological processes and are unable to rule on cause of death. Keeping in mind that temperature primarily guides the postmortem decomposition process, most routine forensic pathological protocol can become abbreviated in as little as 1 week after death. At the other extreme of postmortem time, the biological anthropologist traditionally examines museum collections of prehistoric and historic skeletons that are long devoid of the moist soft-tissue envelope so important to forensic pathology. Their examination involves the odontoskeletal system only and, while they may be able to venture a manner of death, provided there are perimortem traumatic signatures, little else is possible. This is not to imply that pathologists are not astute in the examination of bone or that anthropologists know nothing about soft tissue. By virtue of the research facility, forensic anthropology is now developing a legally defensible battery of expertise to collaborate with
8
forensic pathologists in understanding the complex processes between fresh remains and skeletal remains.
Anthropological Research Facility There has been remarkable progress in our understanding of the complexities of the later postmortem process of soft-tissue decomposition since the late 1970s. Much of this knowledge stems not only from the burgeoning development of forensic anthropology as a discipline within the American Academy of Forensic Sciences and a resource for forensic pathological inquiry, but from the formation and maintenance of an outdoor research facility at the University of Tennessee, USA, where these processes of human soft-tissue decomposition have been studied. William M. Bass envisioned firsthand witnessing of these processes in a natural setting with bodies donated to scientific research. Presently, 600 donations have been received at the research facility. The facility is a wooded 4-acre tract protected by a chain link fence with razor wire and a privacy fence and under constant surveillance. While carnivores are inhibited from inside access, rodents often gain access. The facility provides the unique opportunity to study longitudinally the accumulated effects of decomposition of soft tissues under a wide range of variables, including temperature and humidity, clothing, burial, water submersion, effects of sun exposure, and body posture/ gravity. Also examined are biochemical soil change, odor, and burial/grave testing using ground-penetrating radar technology. Finally, the lion’s share of forensic entomology is derived from facility research. Most of this research has been fueled by collaboration with law enforcement and our attempts to stage research that answers specific problems relating to TSD. This natural laboratory holds a colossal advantage over the cross-sectional exposure provided by isolated decomposition cases introduced to the forensic pathologist. No matter how accurate the assessment of postmortem time may be, after identification the remains are removed for burial/cremation without any
Encyclopedia of Forensic and Legal Medicine, Volume 2
doi:10.1016/B978-0-12-800034-2.00135-X
Death Investigation Systems: Decomposition, Patterns, and Rates
opportunity to study the progression of the events. So, the pathologist gains expertise in soft-tissue decomposition after a career of exposure gaining confidence for testimony. No one doubts the TSD testimony afforded by the senior forensic pathologist armed with a career of cases. However, the resident or new pathologist has little recourse as a result of limited exposure to decomposed bodies and therefore is poorly equipped to render expert opinion. The facility allows examination and appreciation of decomposition daily, weekly, monthly, and even, annually. In a sense, the research facility is one giant validation study. Besides a laboratory to study decomposition, the research facility provides an outdoor classroom for training graduate students in forensic anthropology. The bulk of the research conducted has been formulated through their interests as associated with particular crime-scene events. Also, local, regional, state, and national law enforcement agencies, members of the medicolegal community into whose service the forensic anthropologist is called, as well as canine search and rescue teams, are afforded the training opportunity in clandestine grave discovery and excavation techniques at the research facility. The anthropological research facility contributes to forensic science by enumerating the changes that occur during decomposition of human remains related to temperature and other previously described variables. Through this type of longitudinal study, researchers have determined the sequence of stages through which human remains move to reach the skeletal state. Some of these stages are better correlated with TSD than others, but nonetheless, each body, if allowed to decompose naturally, will eventually undergo each of the following stages.
reticulum by adenosine triphosphate (ATP), but with little or no ATP production at death, increased calcium causes muscle contraction. Rigor starts 2–6 h after death, typically manifested by stiffness in the jaw and neck, and then spreading to the rest of the body over the next 4–6 h and lasting from 24 to 18 h after onset. These temporal estimates are just that, estimates, and pathologists have long recognized situations of delayed onset or abbreviated duration based primarily upon temperature. Similarly, temperature controls the onset, tempo, and duration of the remaining postmortem processes of decomposition. One of the externally visible signs of autolysis is skin slippage. During autolysis, the junction of the epidermis and dermis is weakened by the release of hydrolytic enzymes. This loosening allows the epidermal layer to slip off the dermal layer, giving rise to the term skin slippage (Figure 1). The products liberated by autolysis fuel the next process of decomposition: putrefaction. Putrefaction is the consumption of soft tissues through the exponential proliferation of endogenous enteric bacteria. It is caused by release of acidic autolyzed cellular contents that, along with an almost completely anaerobic environment, creates a perfect environment for bacterial proliferation. This first occurs in the cecum where the largest population of endogenous bacteria is found (Figure 2). Hydrogen sulfide (H2S) gas is a byproduct of this bacterial growth from the interaction with the iron in hemoglobin to form a black precipitate, ferrous sulfide (FeS). This darkening is the agent that discolors the body’s circulatory architecture as intravascular hemolysis/marbling (Figure 3). Initially, other cecal discoloration is caused by the hydrolytic enzymes attacking the biliary system to release biliverdin, bilirubin, and urobilin pigments into the
Stages of Decomposition The biochemical process of internal decomposition begins immediately at clinical death with a process called autolysis. Autolysis is the irreversible cascade of cell death that destroys structural integrity and the cell-tocell junction. Besides leading to widespread tissue necrosis, autolysis triggers three events that produce the three familiar externally visible manifestations: algor, livor, and rigor mortis. Algor mortis is internal cooling of the body to ambient temperature. Livor mortis is the gravitational pooling of blood in the capillary beds of dependent body parts. Initially, livor mortis is ‘unfixed’ and gentle pressure on a livor area will blanch. After 8– 12 h, livor becomes ‘fixed’ as capillary blood begins clotting. Rigor mortis is stiffening of muscles fibers after death, resulting from the flood of calcium ions into the sarcomere (contractile units of the muscle fiber). During life, this calcium is pushed back into the sarcoplasmic
9
Figure 1 Skin slippage on the plantar portion of the foot associated with early decomposition. This phenomenon occurs due to the weakening of the junction between the dermis and epidermis during decomposition, causing the epidermis to slip away from the dermis.
10
Death Investigation Systems: Decomposition, Patterns, and Rates
Figure 2 Purplish-green discoloration in the cecal region of the lower right abdominal quadrant associated with early decomposition caused by the proliferation of endogenous bacteria producing hydrogen sulfide in a nowanerobic environment.
Figure 3 The marbling pattern (intravascular hemolysis) of the circulatory system that appears in early decomposition, caused by the invasion of the circulatory system by hydrogen sulfide gas, producing bacteria. This same process of gas production results in the bloating that is characteristic of the middle stages of decomposition.
abdominal tissues. The bloating stage results from the release of vast amounts of hydrogen sulfide within the body’s organs and cavities from bacterial growth in the anaerobic environment. This gas diffuses with ease through body tissue due to its small molecular structure. Gas accumulation within the body causes distension of the abdomen and swelling of limbs and facial structures (Figure 4).
Insect Activity It is during the bloat phase that insects become a major factor in the modification of tissues. Forensic
Figure 4 An adult male in full bloat 2 weeks postmortem during late spring. Note the extreme expansion of the abdominal cavity causing splitting of the soft tissue of the lateral chest wall. Also note the elevated posture of the pelvic limbs.
entomologists learned that insect growth, feeding, and migration are generally genus-specific and are as driven by temperature, daily and seasonally, as the events of internal biochemical decomposition. Sarcophagic insects and their activity are the litmus test for soft-tissue reactions during decomposition. Insect interest in a dead body is instantaneous upon placement at the Anthropological Research Facility. Blowflies are usually first to arrive, ovipositing in any natural or traumatically created shaded orifice. These include the ears, nostrils, mouth, eyes, hair, and the shaded regions of the genital region and the ground – body interface. At the crime scene, detection of differential decomposition of soft tissues and insect activity in areas other than these regions signals peri- or postmortem trauma that has provided an artificial segue for ovipositing (and subsequent feeding). It is important to realize that, while numerous arthropods habituate the host off and on during the entire decomposition tenure, blowfly larvae (maggots) are responsible for ingesting 95% of the body mass. After eggs hatch, larvae develop through three distinct stages of growth that are termed instars. After the final stage, third-instar maggots migrate away from the body, seeking a dark, cool, subterranean location (or clothing) to generate a pupal casing where they remain until emerging as adult blowflies. The entomologist, using a strategy of collecting a representative sample of maggot sizes on the body to capture growth variation, and looking away from the body for pupal casings, can estimate with confidence the length of time the body has been colonized and thus narrow a postmortem interval. At the beginning of the drying phase, other arthropod species become more interested in the tissues and sites of fluid runoff. These include, but are not exclusive to, dermestid beetles, ants,
Death Investigation Systems: Decomposition, Patterns, and Rates
wasps, and other types of beetle that continue to ingest the drying skin and remaining cartilaginous regions. By determining species, one can identify the most reliable postmortem interval, as some species, for example, will not colonize when the remains are too moist or too dry. As bloat subsides, deflation of the abdomen occurs, with drying of the skin. Drying begins at exposed tissue margins, that is, lips, nose, eyelids, and wounds, besides hands and feet. Generally, on the level of the entire body, drying follows bloat, but specific regions dry more quickly (tissue margins) than the rest of the body. The drying stage refers to the drying of the entire body or large portions of it, not these focal areas. Coincident with drying is rib head and cervical bone exposure. It is not uncommon for the stages of bloat and drying to coincide. If the soft tissues (including skin) have not been destroyed or decomposed by bacteria or arthropods, there are two avenues in which decomposition can proceed in order to reach a skeletonized state: adipocere formation and/or mummification. Adipocere is a white or cream-colored waxy, homogeneous substance derived from body fat that may form during the decomposition of remains in a moist environment, that is, water submersion, damp grave. The chemical process is termed saponification and used interchangeably with adipocere formation. Adipocere formation appears to benefit from a catalyst of alkaline, such as formaldehyde, which is commonly used in embalming fluid. Yet, certain soils are highly alkaline, which also contributes to adipocere formation. Alkaline will hydrolyze the fat, turning it into this soap-like substance. Mummification is the drying of soft tissues to take on a hard, leathery appearance. This is most common in arid areas with low humidity or little precipitation. However, it is the terminal stage in soft-tissue decomposition processes at the anthropological research facility, even though mummification happens more quickly in dry arid environments. The speed with which moisture and fluids evacuate the body is much quicker in an arid environment, though no time estimates can be given due to lack of a research facility in that climate. Complete mummification often occurs in individuals with little body fat since fat can have enough moisture content to prevent complete mummification (Figure 5).
Estimation of Time Since Death Accumulated degree days (ADD) are defined as the total number of degrees accumulated in a given time period, represented by the highest temperature for each period. Thus, the ADD for a week is the highest temperature for each day, added to that of the following day. So, if the temperature is 20 1C each day, the ADD for the week is 140 1C (7 20 ¼ 140). Vass used this measure to track the degree of decomposition, thereby linking
11
Figure 5 An adult male in mummified stage of decomposition (2 months after death) prior to skeletonization.
temperature with time. Essentially, if a body was in x state of decomposition, based on the chemical breakdown of certain lipids, Vass could backtrack the length of time the body had been exposed by adding up the temperatures for the preceding days and comparing that to actualistic studies performed at the facility. This provided a standard for chemical values versus the ADD to be set. This standard would be compared to the chemical values found at a crime scene and the corresponding ADD value could be used to determine the length of TSD. With the ADD value, the TSD estimate is calculated by removing the temperatures from the preceding days until this equals 0. This would give an estimate of the number of days the body had been decomposing in that area. Marks and colleagues used ADD but compared them to stages of decomposition. The ADD was not consistent across decomposition stages and the researchers were hard-pressed to get narrowed ADD estimates to fall within single decomposition stages for everybody. Instead, there was an overlap of overlap upon different stages of decomposition. The problem may be that ADD is not representative of the ‘amount’ of accumulated temperature and does not take into account the 24-h temperature fluctuations. Vass also recognized this and attempted to correct it by adjusting ADD to cumulative degree hours (CDH). This measure represents an average value of each 12-h period (the high þ the low/2). Thus, if temperature is 10 1C at 12 p.m. and 0 1C at 12 a.m., the CDH would be 5. For one day, there are two calculations of CDH (one for each 12-h period). We have found that this procedure does not adequately characterize the temperature fluctuations in a 24-h period either, and, if a body decomposition scene is not covered by a temperature gauge, then it is virtually unusable. These problems are currently being resolved through ongoing facility experimentation.
12
Death Investigation Systems: Decomposition, Patterns, and Rates
Figure 6 A woman in differential decomposition. Note the advanced state of decomposition of the head, which has been completely blackened, while the rest of the body retains a near-natural skin color.
This plethora of research in determining TSD implies that there are many circumstances and variables that affect postmortem interval estimation. It is by no means an exact science but rather an approximation. One major result of this longitudinal study affords the researcher the luxury of seeing commonality between the decomposition processes of each body and more importantly, the ability to discern where the normal process of decomposition has been compromised or altered. Nowhere is this more applicable than in forensic cases that display differential decomposition. Differential decomposition is the term used to describe a situation where one body exhibits different stages of decomposition in different parts of the body. It is paramount for a forensic anthropologist to determine what caused this differentiation. For example, Figure 6 depicts a forensic case where the body of a woman was found in a wooded area. It is clear that her head is in a more advanced state of decomposition than the rest of her body. The goal is to determine why the head has moved more quickly through the decomposition phases, or perhaps, why the decomposition of the rest of the body has been retarded.
Conclusion We realize that the process of decomposition is regionally variable: temperatures and humidity that guide decomposition in the southeast will probably not apply to other regions of the USA. However, all bodies will go through the same itemized changes. Decomposition will
not skip stages, but the specific chronology of change will vary slightly from victim to victim based on other variables. It is important to realize that, regardless of location in postmortem time, decipherment of human decomposition will never be an exact science. Like growth and development, decomposition is biological continuum that cannot be easily quantified and qualified. Hence, understanding the deterioration of multiple criteria is necessary to best satisfy our curiosity. The anthropological research facility provides a unique opportunity to understand the processes of human soft-tissue decomposition and the research agenda is partially fueled by collaboration and consultation within the medicolegal community. The research potential of the facility, not unlike a crime scene, provides a crossroads where the perspectives of many forensic investigators intersect and flourish.
See also: Anthropology: Morphological Age Estimation. Anthropology: Sex Determination. Entomology. Postmortem Changes: Overview
Further Reading Bass, W.M., Jefferson, J., 2003. Death’s Acre: Inside the Legendary Forensic Lab the Body Farm Where the Dead Do Tell Tales. New York, NY: G.P. Putnam’s Sons. Byrd, J.H., Castner, J.L. (Eds.), 2001. Forensic Entomology − The Utility of Arthropods in Legal Investigations. Boca Raton, FL: CRC Press. Catts, E.P., Haskell, N.H., 1990. Entomology and Death − A Procedural Guide. Clemson, SC: Joyce’s Print Shop. Love, J.C., 2001. Evaluation of decay odor as a time since death indicator. Thesis, University of Tennessee, Hodges Library/Thesis/Dissertation. Love, J.C., Marks, M.K., 2003. Taphonomy and time: Estimating the postmortem interval. In: Steadman, D.E. (Ed.), Hard Evidence: Case Studies in Physical Anthropology. Upper Saddle River, NJ: Prentice-Hall, pp. 160–175. Marks, M.K., Love, J.C., Elkins, S.K., 2000. Time since death: A practical guide to physical postmortem events. American Journal of Forensic Science Proceedings, 181–182. Miller, M.L., 2002. Coupling ground penetrating radar applications with continually changing decomposing human targets: An effort to enhance search strategies of buried human remains. Thesis, University of Tennessee. Hodges Library/ Electronic Thesis. Miller R.A., 2002. The affects of clothing on human decomposition: Implications for estimating time since death. Thesis, University of Tennessee. Hodges Library/ Thesis/Dissertation. O’Brien, T.G., 1995. Human soft-tissue decomposition in an aquatic environment and its transformation into adipocere. In: Proceedings of the 47th Annual Meeting of the American Academy of Forensic Sciences, 13-18 February, pp. 155−156. Seattle, WA; Colorado Springs, CO: American Academy of Forensic Sciences. Srnka, C.F., 2003. The effects of sun and shade on the early stages of human decomposition. Thesis, University of Tennessee. Hodges Library/Thesis/ Dissertation. Vass, A.A., 1992. Time since death determinations of human cadavers utilizing soil solution. Thesis, University of Tennessee. Hodges Library/Thesis.