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Determination of age of fingerprints
Forensic Science International, 46 (1990) 133- 137 Elsevier Scientific Publishers Ireland Ltd.
DETERMINATION
133
OF AGE OF FINGERPRINTS
KRYSTYNA BANIUK Dactyloscopy Department of the Main Police Headquarters,
Warsaw lPolund
Summary In this paper the process of ageing of fingerprints is considered and such factors affecting the process as: chemical composition of a fingerprint trace, external influences and background material are taken into account. On the basis of experience accumulated over a long period of time standards have been set allowing the determination of the time span during which traces of different chemical compositions stored in various ambient conditions can be effectively used for dactyloscopic purposes. In the closing part of the paper the efficiency of the method and usefulness of the results obtained are presented. Key words: Fingerprints; Age determination; Methods
The problem of evaluation of the age of fingerprints are one of the most difficult issues in criminalistics being, at the same time, very important from the point of view of criminal proceedings. The age of fingerprints is of paramount importance here. These traces are most frequently found at the scene of the crime and without the possibility of evaluation of their age the evidential value of the classical dactyloscopic experise would be in many cases rather dubious. As long ago as in 1970, at the Dactyloscopy Department, the method of evaluating the age of fingerprint traces was worked out and has routinely been used up to the present moment. It concerns the traces appearing on a smooth and non-absorptive surface, both in an open and enclosed space. The bases for infering the age of fingerprint traces at the scene of the crime are as follows: -
-
-
reconstruction of the conditions in which the evidential traces were formed, comparative examination of evidential traces with fingerprints of the suspect (accused) which have undergone experimental examination concerning ageing in a given environment, knowledge and experience of an expert in the field of skin physiology and in the mechanism of formation and ageing of fingerprints.
The reconstruction of conditions in which the fingerprints constituting the body of evidence in a given case were formed is possible from the information contained in the report made at the scene of the crime, concerning the 0379-0738/90/$03.50
0 1990 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
134
characteristic features of the environment in which the traces had remained until they were discovered and transferred into foil, the kind of surface, etc. Knowing the mechanism of fingerprints formation is an indispensable factor to support an opinion concerning the age of fingerprints. An expert should know what properties of the surface make it more difficult for legible fingerpints to be formed, or whether, for example, the poor legibility of the trace is the result of a loss of stickiness of the trace due to its ageing or, perhaps, of too weak a pressure of the finger on the surface. Over the years, empirical examination carried out at the Department of Criminalistics in the subject of the age of fingerprint traces has shown that each trace is subjected to the ageing process from the moment of its formation. The ageing of fingerprint traces encompasses both the changes in the sweat-grease substance and in the picture itself of the traces in a given period and under the influence of different factors. The rate and the actual development of the ageing process depend on the qualitative and quantitative composition of the sweat-grease substance, the kind of surface on which a given trace appears, and on atmospheric conditions (temperature, humidity, air pollution, rainfalls, etc.). The content of grease components in sweat plays a major role in the ageing process of fingerprint traces. The average time during which these traces remain in an identifiable state is five times longer in the case of traces with a considerable content of grease components in the grease-sweat substance than in the case of so-called sweat traces, deprived of grease components. The relation between the durability of fingerprint traces and the chemical composition of the grease-sweat substance appears to exist both in the case of traces found in an open space, as well as in an enclosed one. The research concerning the ageing process of fingerprint traces in both kinds of environment has not only provided many observations as to the behaviour of the traces influenced by temperature, humidity and other atmospheric conditions, but also, and maybe above all, has made it possible to get to known the mechanism of the ageing process and the factors enhancing and delaying its development, and to establish a correlation between the durability of the fingerprint traces and environmental factors. This correlation, in an environment with changeable atmospheric conditions having a direct influence on the traces, is more easily observable, especially when these conditions become extreme. What is decisive here is the cumulative action of all environmental factors. The durability of fingerprint traces also depends on physical and chemical properties of the surface. Surfaces which are smooth and non-absorptive such as glass, metals, china, and some kinds of plastic materials are conducive to good preservation of fingerprint traces for a long time, as opposed to rough and absorptive surfaces where their unevenness causes the sweat and grease substance to spill over, and be absorbed by the capillary vessels of the inner structure of the surface to absorb it.
A change in the rate of ageing process can occur in its every stage. Here are some of the factors enhancing the ageing process: temperature above 37OC, low humidity of the air (below 30°,b1, precipitation, light and air pollution. On the other hand temperatures below O°C and a high content of grease compounds in the sweat-grease substance have a delaying effect. The ageing process can be divided into two stages: (11 Drying of the sweat-grease substance, (21 Loss of the legibility of the traces. In the first stage the following phases can be differentiated: -
Dulling of the sweat-grease substance, Loss of stickiness, Narrowing of the fingerprints, Loss of the continuity of the fingerprints.
The last phase concerns exclusively sweat traces, when the process of drying has been considerably enhanced, e.g. fingerprints on a light-bulb. The advancement of the ageing process is shown by changes in the picture of a fingerprint trace such as: narrowing of fingerprints, loss of their continuity, dustiness of the area between the prints and the reaction of the trace to dactyloscopic powders. These changes appear in succession and are characteristic of particular stages of the ageing process. Hence their name - age traits of the fingerprint traces. The number and kind of trait provides information on whether the trace under examination is fresh or old. During evaluation of the age of fingerprint traces one should bear in mind the existence of seemingly fresh and seemingly old traces whose properties are inconsistent with their real age: e.g. a sweat trace on a glass surface, revealed after a temperature of 200°C has acted on the surface for 5 min looks like an old trace, because fingerprints have the shape of continuum of points made of solid components of the sweat of both organic and inorganic origin, after the water has evaporated from the sweat. A trace of this kind, in an enclosed space, at the temperature of 20°C can last in a good condition for about three months. On the basis of the years of empirical research carried out at the Department of Dactyloscopy at Civic Militia Headquarters, during which 20,000 traces were examined, the average time of the persistence of sweat and sweat-grease fingerprint traces on different surfaces, in both kinds of environment (open and enclosed space) has been calculated. Norms of “life-spans” of the traces in different conditions together with a reconstruction of the environment provide the basis to make conclusions concerning the age of fingerprint traces. The comparative material on which to base the age of fingerprint traces is usually obtained as a result of an experiment during which samples of colourless, fingerprint traces are taken off a suspect (accused1 by means of
136
grease-sweat substance and then those traces undergo the natural process of ageing. The way in which samples of fingerprint traces are taken, the kind of surface, time and storage conditions of the comparative samples depend on the circumstances accompanying the formation of traces in evidence. Examination of the age of fingerprint traces starts with an analysis whose aim is to establish whether there exist in the evidence material so-called age traits of the traces, that is, characteristic properties for the stages of the ageing process. The next stage of the research is to relate the degree of advancement of the ageing process with comparative samples and then to ascertain common and different properties which have appeared during the ageing process and to establish the probable time in which the traces were made. The latest technological developments are used to examine the age of fingerprint traces. A videocomparator is used to analyse the picture of fingerprint traces. It makes it possible to enlarge the comparative pictures several times and to overlap them. Computer techniques are used in formulating conclusions concerning the age of fingerprint traces. For this purpose, a computerised set of data concerning the qualitative composition of sweat-grease substance, characteristic features of environment (season of the year, temperature and humidity of the air, precipitation, etc.), physical and chemical properties of the surfaces, etc. norms of average life-spans of fingerprint traces in different conditions, as well as the values describing deviations from these norms in extreme storage conditions have been stored in the computer memory. The lo-year practice of the Department of Dactyloscopy of the Civic Militia Headquarters in this expertise based on its own method makes it possible to evaluate its usefulness in evidence-gathering and investigation process and the degree of usability of its kind of expertise in both preliminary and court proceedings. Over 10 years, more than 100 expert opinions on fingerprint traces have been made at the Department of Dactyloscopy in which: in 88%, due to the expert’s opinion, the version concerning the time when the fingerprint traces were left at the scene of the crime given by the accused was rejected, - in 10% the version given by the accused was confirmed, as a result of which he was acquitted by the court, - in 5% there was no basis to formulate a precise opinion. The data, available to the expert, made it impossible either to confirm or reject one of the two versions concerning the time when the trace was left.
-
Ninety-five out of 100 expertises on the age of fingerprint traces made at the Department of Dactyloscopy were included by the courts in the evidence material which could be found in courts’ opinions.
137
Nevertheless, one should underline that the possibilities of establishing the time when the fingerprint traces were left are not fully used in preliminary and court proceedings. Requests for an expertise of the age of fingerprint traces when the investigation does not yield results seem to be exceptional. An investigator should make sure if fingerprint traces are related to the crime and whether the traces are fresh or old. The method of establishing the age of fingerprint traces worked out at the Department of Dactyloscopy of the Civic Militia Headquarters can be further developed and perfected. When all the changes occurring in the sweat-grease substance during the ageing process have been ascertained, the method may be fully used. As of now, the problem has not been solved anywhere in the world. Although research of the sweat-grease substance by means of liquid chromatography and thin-layer chromatography with the use of argon laser has been carried out it turned out to be impractical as the analysis needs sweat samples in considerable quantity.
DETERMINATION
133
OF AGE OF FINGERPRINTS
KRYSTYNA BANIUK Dactyloscopy Department of the Main Police Headquarters,
Warsaw lPolund
Summary In this paper the process of ageing of fingerprints is considered and such factors affecting the process as: chemical composition of a fingerprint trace, external influences and background material are taken into account. On the basis of experience accumulated over a long period of time standards have been set allowing the determination of the time span during which traces of different chemical compositions stored in various ambient conditions can be effectively used for dactyloscopic purposes. In the closing part of the paper the efficiency of the method and usefulness of the results obtained are presented. Key words: Fingerprints; Age determination; Methods
The problem of evaluation of the age of fingerprints are one of the most difficult issues in criminalistics being, at the same time, very important from the point of view of criminal proceedings. The age of fingerprints is of paramount importance here. These traces are most frequently found at the scene of the crime and without the possibility of evaluation of their age the evidential value of the classical dactyloscopic experise would be in many cases rather dubious. As long ago as in 1970, at the Dactyloscopy Department, the method of evaluating the age of fingerprint traces was worked out and has routinely been used up to the present moment. It concerns the traces appearing on a smooth and non-absorptive surface, both in an open and enclosed space. The bases for infering the age of fingerprint traces at the scene of the crime are as follows: -
-
-
reconstruction of the conditions in which the evidential traces were formed, comparative examination of evidential traces with fingerprints of the suspect (accused) which have undergone experimental examination concerning ageing in a given environment, knowledge and experience of an expert in the field of skin physiology and in the mechanism of formation and ageing of fingerprints.
The reconstruction of conditions in which the fingerprints constituting the body of evidence in a given case were formed is possible from the information contained in the report made at the scene of the crime, concerning the 0379-0738/90/$03.50
0 1990 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
134
characteristic features of the environment in which the traces had remained until they were discovered and transferred into foil, the kind of surface, etc. Knowing the mechanism of fingerprints formation is an indispensable factor to support an opinion concerning the age of fingerprints. An expert should know what properties of the surface make it more difficult for legible fingerpints to be formed, or whether, for example, the poor legibility of the trace is the result of a loss of stickiness of the trace due to its ageing or, perhaps, of too weak a pressure of the finger on the surface. Over the years, empirical examination carried out at the Department of Criminalistics in the subject of the age of fingerprint traces has shown that each trace is subjected to the ageing process from the moment of its formation. The ageing of fingerprint traces encompasses both the changes in the sweat-grease substance and in the picture itself of the traces in a given period and under the influence of different factors. The rate and the actual development of the ageing process depend on the qualitative and quantitative composition of the sweat-grease substance, the kind of surface on which a given trace appears, and on atmospheric conditions (temperature, humidity, air pollution, rainfalls, etc.). The content of grease components in sweat plays a major role in the ageing process of fingerprint traces. The average time during which these traces remain in an identifiable state is five times longer in the case of traces with a considerable content of grease components in the grease-sweat substance than in the case of so-called sweat traces, deprived of grease components. The relation between the durability of fingerprint traces and the chemical composition of the grease-sweat substance appears to exist both in the case of traces found in an open space, as well as in an enclosed one. The research concerning the ageing process of fingerprint traces in both kinds of environment has not only provided many observations as to the behaviour of the traces influenced by temperature, humidity and other atmospheric conditions, but also, and maybe above all, has made it possible to get to known the mechanism of the ageing process and the factors enhancing and delaying its development, and to establish a correlation between the durability of the fingerprint traces and environmental factors. This correlation, in an environment with changeable atmospheric conditions having a direct influence on the traces, is more easily observable, especially when these conditions become extreme. What is decisive here is the cumulative action of all environmental factors. The durability of fingerprint traces also depends on physical and chemical properties of the surface. Surfaces which are smooth and non-absorptive such as glass, metals, china, and some kinds of plastic materials are conducive to good preservation of fingerprint traces for a long time, as opposed to rough and absorptive surfaces where their unevenness causes the sweat and grease substance to spill over, and be absorbed by the capillary vessels of the inner structure of the surface to absorb it.
A change in the rate of ageing process can occur in its every stage. Here are some of the factors enhancing the ageing process: temperature above 37OC, low humidity of the air (below 30°,b1, precipitation, light and air pollution. On the other hand temperatures below O°C and a high content of grease compounds in the sweat-grease substance have a delaying effect. The ageing process can be divided into two stages: (11 Drying of the sweat-grease substance, (21 Loss of the legibility of the traces. In the first stage the following phases can be differentiated: -
Dulling of the sweat-grease substance, Loss of stickiness, Narrowing of the fingerprints, Loss of the continuity of the fingerprints.
The last phase concerns exclusively sweat traces, when the process of drying has been considerably enhanced, e.g. fingerprints on a light-bulb. The advancement of the ageing process is shown by changes in the picture of a fingerprint trace such as: narrowing of fingerprints, loss of their continuity, dustiness of the area between the prints and the reaction of the trace to dactyloscopic powders. These changes appear in succession and are characteristic of particular stages of the ageing process. Hence their name - age traits of the fingerprint traces. The number and kind of trait provides information on whether the trace under examination is fresh or old. During evaluation of the age of fingerprint traces one should bear in mind the existence of seemingly fresh and seemingly old traces whose properties are inconsistent with their real age: e.g. a sweat trace on a glass surface, revealed after a temperature of 200°C has acted on the surface for 5 min looks like an old trace, because fingerprints have the shape of continuum of points made of solid components of the sweat of both organic and inorganic origin, after the water has evaporated from the sweat. A trace of this kind, in an enclosed space, at the temperature of 20°C can last in a good condition for about three months. On the basis of the years of empirical research carried out at the Department of Dactyloscopy at Civic Militia Headquarters, during which 20,000 traces were examined, the average time of the persistence of sweat and sweat-grease fingerprint traces on different surfaces, in both kinds of environment (open and enclosed space) has been calculated. Norms of “life-spans” of the traces in different conditions together with a reconstruction of the environment provide the basis to make conclusions concerning the age of fingerprint traces. The comparative material on which to base the age of fingerprint traces is usually obtained as a result of an experiment during which samples of colourless, fingerprint traces are taken off a suspect (accused1 by means of
136
grease-sweat substance and then those traces undergo the natural process of ageing. The way in which samples of fingerprint traces are taken, the kind of surface, time and storage conditions of the comparative samples depend on the circumstances accompanying the formation of traces in evidence. Examination of the age of fingerprint traces starts with an analysis whose aim is to establish whether there exist in the evidence material so-called age traits of the traces, that is, characteristic properties for the stages of the ageing process. The next stage of the research is to relate the degree of advancement of the ageing process with comparative samples and then to ascertain common and different properties which have appeared during the ageing process and to establish the probable time in which the traces were made. The latest technological developments are used to examine the age of fingerprint traces. A videocomparator is used to analyse the picture of fingerprint traces. It makes it possible to enlarge the comparative pictures several times and to overlap them. Computer techniques are used in formulating conclusions concerning the age of fingerprint traces. For this purpose, a computerised set of data concerning the qualitative composition of sweat-grease substance, characteristic features of environment (season of the year, temperature and humidity of the air, precipitation, etc.), physical and chemical properties of the surfaces, etc. norms of average life-spans of fingerprint traces in different conditions, as well as the values describing deviations from these norms in extreme storage conditions have been stored in the computer memory. The lo-year practice of the Department of Dactyloscopy of the Civic Militia Headquarters in this expertise based on its own method makes it possible to evaluate its usefulness in evidence-gathering and investigation process and the degree of usability of its kind of expertise in both preliminary and court proceedings. Over 10 years, more than 100 expert opinions on fingerprint traces have been made at the Department of Dactyloscopy in which: in 88%, due to the expert’s opinion, the version concerning the time when the fingerprint traces were left at the scene of the crime given by the accused was rejected, - in 10% the version given by the accused was confirmed, as a result of which he was acquitted by the court, - in 5% there was no basis to formulate a precise opinion. The data, available to the expert, made it impossible either to confirm or reject one of the two versions concerning the time when the trace was left.
-
Ninety-five out of 100 expertises on the age of fingerprint traces made at the Department of Dactyloscopy were included by the courts in the evidence material which could be found in courts’ opinions.
137
Nevertheless, one should underline that the possibilities of establishing the time when the fingerprint traces were left are not fully used in preliminary and court proceedings. Requests for an expertise of the age of fingerprint traces when the investigation does not yield results seem to be exceptional. An investigator should make sure if fingerprint traces are related to the crime and whether the traces are fresh or old. The method of establishing the age of fingerprint traces worked out at the Department of Dactyloscopy of the Civic Militia Headquarters can be further developed and perfected. When all the changes occurring in the sweat-grease substance during the ageing process have been ascertained, the method may be fully used. As of now, the problem has not been solved anywhere in the world. Although research of the sweat-grease substance by means of liquid chromatography and thin-layer chromatography with the use of argon laser has been carried out it turned out to be impractical as the analysis needs sweat samples in considerable quantity.