Forensic examination of stolen-recovered vehicles

CHAPTER

4

Part II: Chemical Traces—Drugs, Explosives, and Gunshot Residue Francesco Saverio Romolo

4.9

INTRODUCTION

Motor vehicles are often used in the commission of crimes and are found in criminal activities such as transporting drugs, explosives, and firearms. In these cases the forensic scientist can look for chemical traces due to a transfer from the source to the vehicle. This transfer is a phenomenon of capital importance in forensic science, generally known as the principle of exchange of Locard [1]. There are three major classes of chemical traces described in this chapter that could have some probative value in solving a crime: drugs, explosives, and gunshot residue. The detection of the presence of drugs, explosives, or gunshot residue can represent very important evidence in the investigation of a crime.

4.10 C H E M I C A L TRACES 4.10.1 Illicit Drugs Drugs and explosives are mainly solid materials. Particles can be transferred during any contact with a receiving surface or can fall on the floor of the car or in the cargo area of a truck. In the past, most drugs were made from plants, such as the coca bush for cocaine, opium poppies for heroin, and cannabis for hashish or marijuana. According to the United Nations Office on Drugs and Crime data from 95 countries, in 2003, 52% of the seizures were related to cannabis, 25% involved opiates, 10% involved amphetamines, and 7% involved cocaine [2]. There are two main forms in which cannabis is consumed: herbal cannabis and cannabis resin. The former comprises the flowering tops and leaves of the plant. Cannabis resin is popularly referred to as hashish and consists of the secretions of the plant created in the flowering phase of its development. Pure cocaine and pure heroin are white or colorless crystalline powders, but street heroin samples can be brown because of insufficient purification procedures. In the last decade, the most significant trend has been the increase in the number of seizures of amphetamine-type stimulants. Global amphetamine-type stimulant production is currently above 400 tons, three quarters of which is either methamphetamine or amphetamine and one quarter of which is "ecstasy" [2]. Amphetamine-type stimulants are generally found in solid form as powder or tablets. Physical aspect and physicochemical properties of the different compounds are important for their recognition and for their detection (Table 4-1) [3].

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Table 4-1 Illicit Drugs: properties of pure compounds [3]. Compound

Formula

Molecular weight [g/mol]

Amphetamine

C9H13N

135

Liquid

—

Amphetamine phosphate

C9H13N, H3PO4

233

Solid

Decomposes at about 300°C

Amphetamine sulfate

(C9Hi3N)2, H2SO4

368

Solid

Above 300°C with decomposition

Cocaine

Q7H21N04

303

Solid

98°C

Cocaine hydrochloride

C17H21NO4, H C I

339

Solid

About 195°C with decomposition

Heroin

C21H23NO5

369

Solid Solid

173°C 229°C to 233°C

Physical state

Melting point

Heroin hydrochloride

C21H23NO5, H C I , H2O

423

Methamphetamine

C10H15N

149

Liquid

—

Methamphetamine hydrochloride Methylenedioxymethamphetamine (MDMA, Ecstasy)

Q0H15N, HCI

185

C11H15NO2

193

Solid Liquid

—

Methylenedioxymethamphetamine hydrochloride (MDMA, Ecstasy)

C11H15NO2, H C I

230

Solid

147°Cto 153°C

170°Cto 175°C

4.10.2 Explosives Trace detection of explosives and drugs is generally dependent on their vapor pressure, that is, their ability to generate vapors at a given temperature in equilibrium above the solid (or liquid) phase. These data have been thoroughly studied for explosives and are included in Table 4-2, along with other physicochemical properties [4]. Most of the high explosives and all the inorganic compounds in black powder and pyrotechnical mixtures are solid. Nitroglycerine (NG) and ethyleneglycoldinitrate (EGDN) are liquid at room temperature but are always mixed with other compounds in commercial products. Nitrocellulose (NC) allows NG (and EGDN) to form a gelatinous mixture. One of the strongest commercial explosives is called blasting gelatin and consists of 92% to 94% NG gelatinized with 6% to 8% of a special type of NC, called guncotton [5]. In some applications, called extra dynamites or extra gelatin dynamites, a fuel/oxidizer mixture is added to the composition. Fuels such as sawdust or wood meal (fine sawdust) and oxidizers such as sodium nitrate or, more often, ammonium nitrate are typically used. NG can also be used in some smokeless powders. Smokeless powders are low explosives, used in firearms as propellants for projectiles. The composition of smokeless powders can be distinguished between single-base powders (NC), double-base powders (NC plus NG), or triple-base powders (NC, NG, nitroguanidine). In propellant manufacturing one or more additives are always used, such as dinitrotoluenes (DNT), diphenylamine(DPA), or ethylcentralite

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Table 4-2 Explosives: properties of pure compounds [4]. Compound

Molecular formula

Molecular weight [g/mol]

Physical state

Melting point [°C]

Temperature of explosion [°C]

Vapor pressure at 20°C [Pa]

Ethyleneglycoldinitrate (EGDN)

C2H4N2O6

152

Liquid

—

237

5.1

Nitroglycerine (NG) Triacetone triperoxide (TATP)

C3H5N3O9

227

Solid

222

Solid

13 94

270 227

0.03-0.2

CgHisOe

2,4-Dinitrotoluene (2,4-DNT)

C7H6N2O4

182

Solid

69

270

2.5

2,4,6-Trinitrotoluene (TNT)

C7H5N3O6

227

Solid

81

288

0.001

Pentaerythritoltetratrinitrate (PETN)

C5H8N4O12

316

Solid

141

210

1 to 8 X 10-'

Cyclotrimethylenetrinitramine (RDX)

CsHeNeOe

222

Solid

204

217

1 t o 4 x 10"'

0.4

Table 4-3 Typical formulations of some smokeless powders produced in the United States [6]. Composition [%] Type

NC

NG

— —

Single base M6

87

Single base MIO

98

Double base M2 Double base M5

77.45 81.95

Double base M8

52.15

19.5 15.0 43.0

Double base M21 Double base N5 Double base MDM

53.0 50.0 48.6

31.0 34.9 27.0

DNT

DPA

EC

10 0.6 0.6 0.6 2.0 1.1

Totals might not reach 100% because only the components of forensic interest are presented.

(EC). Table 4-3 shows the main components in typical formulations of several smokeless powders produced in the United States [6]. These explosives can transfer traces of NG and EGDN through vapor due to their high vapor pressure, leaving traces behind without the necessity of a direct contact. Another explosive that can leave traces due to vapor transfer is triacetone triperoxide (TATP). It is an explosive in solid form that undergoes substantial sublimation [7]. There are other explosives containing volatile compounds or mixtures, such as ammonium nitrate fuel oil (ANFO) or emulsion explosives, where diesel or other hydrocarbons are present [5].

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4.70.3 Gunshot Residue Chemical traces from firearms are generally called gunshot residue (GSR), cartridge discharge residue, or firearms discharge residue. GSRs are produced when a firearm cartridge is shot. They are composed of burned and unburned particles from the propulsive charge, traces from all the cartridge components, such as the primer, the case, or the bullet, and from the firearm itself. These particles leave the firearm mainly through the muzzle, but a great amount of GSRs passes through the ejection port in semiautomatic and automatic weapons. Also, they can escape through narrow passages, such as the breech end of the barrel in revolvers. If GSRs are found on a specific surface, it was in contact with a GSR source (firearm, spent cartridge case, etc.) or was in the proximity of a firearm at the time of the shooting [8, 9].

4.11 CRIME SCENE E X A M I N A T I O N 4.11.1 Security Phase When a motor vehicle is found and is suspected to be associated with a crime, it must be treated as a scene of crime, including its surrounding area. Before starting any activity, it is necessary to acquire information about the case, particularly for security reasons. A car used by terrorists can be booby-trapped, requiring the intervention of the improvised explosive device (lED) specialists. A truck transporting dangerous material (e.g., radioactive waste) requires the intervention of different specialists at the scene to guarantee the safety of the public and responders. During this preliminary activity, the access to the area surrounding the vehicle must be controlled. As long as a danger exists, forensic issues cannot be fulfilled if they are incompatible with security concerns. Forensic experts may start recording (e.g., video, photographs, sketches) from a safe place before taking control of the zone.

4.77.2 Forensic Phase A: Outside the Vehicle The vehicle can be considered to be both a scene of crime and evidence. Evidence that is not protected from alteration may not provide useful information. In case of bad weather conditions or damage to the vehicle (e.g., broken windows), it can be protected using a tent or some plastic sheeting or can be transported to a special location for subsequent examination in optimal conditions. It is important to carefully consider the modifications brought to the vehicle due to protection activities. Protective plastic sheets should not be placed in contact with the vehicle without examining its external surface first. More severe destruction of evidence could occur when moving the vehicle. If someone has to penetrate the vehicle to move it, he or she should wear appropriate personal protective equipment (PPE) such as mask, scene suit, gloves, boots, and head cover to prevent any risk of contamination.

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Although wearing disposable PPE reduces or eliminates the risk of depositing hairs, fibers, DNA, or trace material from a person's clothing inside the vehicle, it could also destroy evidence such as latent footwear marks or fingermarks. For this reason, any activity inside the motor vehicle during the examination phase must be carefully considered and avoided if unnecessary. Thus, any activity that can be performed properly at the scene without moving the vehicle should be done at the site. Also, before any internal examination of the vehicle, a thorough examination of the external surfaces of the vehicle must be conducted. After examination, photography, and note taking of the outside of the motor vehicle, it might be necessary to proceed to some evidence sampling. General sampling procedures for chemical traces are described later in this chapter; however, a specific procedure for the exterior is adopted for shooting distance determination. The nitrite ions and smokeless powder residues around the bullet entrance hole can be transferred onto an adhesive sheet. After the transfer, lead and copper deposits around the hole can be visualized by spraying suitable reagents directly on the target. The adhesive sheet is examined later in the laboratory using the modified Griess test (MGT) after alkaline hydrolysis of the residues [10].

4.11.3 Forensic Phase B: Vehicle Entrance The area surrounding the vehicle may be a public space where a full contamination control procedure cannot be reasonably adopted. Thus, the potential contamination of the inside of the motor vehicle must always be taken into account and its occurence must be reduced to a minimum. A contamination control procedure should include a decontamination zone where disposable PPE can be correctly suited on, blank samples can be taken, and crime scene equipment can be cleaned before being used in the vehicle. A blank sample should be taken on disposable gloves and jumpsuit after being suited on the crime scene officer and before entering the vehicle in every search for chemical traces. These blank samples should be analyzed with all other samples taken inside the vehicle. They help to ensure that analytical results were not due to contamination coming from the personnel attending the scene or the surrounding environment. If on-site analysis can be conducted, the apparatus should be set up between the decontamination area and the vehicle. In the same decontamination area, crime scene equipment can be decontaminated after use and disposable PPE can be discarded.

4.11.4 Forensic Phase C: On-Site Analysis There are several instruments developed for airport and border control that can be transported to a scene. Some instruments can detect both contraband drugs and explosive vapors, and other apparatus are only explosive vapor detectors (EVD). Until the early 1970s, most EVD were based upon gas chromatography (GC) with electron capture detection (ECD). Because of the low selectivity of the electron capture detector, these instruments exhibited

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a high rate of false alarms. At that time, vapor detection systems based upon ion mobility spectrometry (IMS) started to appear on the market. IMS is a highly sensitive analytical technique able to detect a wide range of chemical compounds (both organic and inorganic) at trace levels in the gas phase. The potential use of IMS for the detection of contraband drugs was discovered almost since the advent of the technique [11]. After the explosion of Pan Am flight 103 over the Scottish town of Lockerbie, high throughput rugged detectors for airport security (based upon IMS) were developed to detect explosive particles rather than vapors [12]. Also, thousands of handheld IMS systems were used in the Gulf War in 1990 and 1991 to detect chemical warfare agents [13]. Thermedics Incorporated (Woburn, Massachusetts) developed a system for the detection of explosive traces mainly for airport security activities, commercialized under the name of EGIS. It is based upon high-speed GC combined with a highly selective and sensitive chemiluminescence detector (CD). It is probably the only well-functioning, but very expensive, instrument available on the market that is based upon the GC-CD technology [14]. There are several comparative studies about commercial on-site apparatus for both explosives and illict drugs [15-17]. All these systems can be handheld, or they include a sampling device that can trap traces onto a suitable substrate and a desorption heater that thermally desorbs traces into the analytical apparatus. In a forensic setting, it is important to understand that the systems described for on-site detection only produce indicative results that must be confirmed in the laboratory with specific analytical techniques. Figure 4-31 shows members the on-site IMS apparatus used by members of the Ecole des Sciences Criminelles of the University of Lausanne in Switzerland.

Figure 4-31 The on-site IMS apparatus used by the members of the Ecole des Sciences Criminelles of the University of Lausanne (Switzerland) close to a vehicle to be examined.

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4.11.5 Forensic Phase D: Sampling Initially, when examining the inside of a motor vehicle, attention should be paid to the collection of clearly visible and macroscopic items that can be recovered by hand with the use of tweezers or small brushes. It is not possible to proclaim a rule as to the order of collection of items that is suitable for all types of evidence. Activities inside the vehicle can damage latent fingermarks; however, the use of powders for such marks can create problems for the sampling of chemical traces. Specialists should carefully evaluate the case to decide the correct order of activities inside the car and should enter the vehicle only after well-thought out planning. The choice of a correct sampling technique is critical for the proper detection and identification of chemical traces and must be decided during the planning. The sampling method depends on several factors, including the nature of the compounds sought, the type and area of the surfaces under examination, and the analytical techniques used for the detection and confirmatory analysis. Chemical traces can be sampled by using one of the techniques described hereafter. Al Gas Trapping When using the gas trapping technique, samples are collected by drawing a known volume of air through a trap. The trap can be a sampling tube containing a suitable material such as Tenax resin [18]. Samples can be desorbed and analyzed either on-site to get preliminary results or in the laboratory. Gas trapping can be used for explosives with high vapor pressure such as EGDN, NG, and TATP. This sampling technique is particularly useful when large volumes are examined, such as inside the cargo area of a truck. The main advantage of gas trapping is the minimal activity required inside the vehicle. Large amounts of air can be drawn from a little hole, without the need for the examiner to enter the volume to be sampled. The main disadvantage of this technique is its lack of sensitivity, particularly with explosives or drugs that exhibits very low vapor pressure. B/ Swabbing Swabbing is the method of choice to work on tables, floors, and smooth fabrics such as leather or plastic. It is difficult to evaluate which is the best swabbing system. Different materials for swabbing are often used: cotton balls, synthetic wool, filter paper, nonwoven cotton cloth, and Acrilan. An ideal swabbing system should efficiently remove the traces from the surface with as little coextracted interfering compounds as possible. Swabs are generally used to collect particulate matter before being thermally desorbed into an IMS system on-site or in another desorption system later in the laboratory, mainly for GC analysis. The sample is taken by firmly rubbing the area several times, using hands, tweezers, or a specifically designed swab holder. Figure 4-32 shows an example of a commercial swab prewetted by isopropanol and water being used to sample a surface [19]. If a wet swab is used, it must be ensured that the sampled compounds remain stable in the solvent used for the swab. For example, when in water solution, some explosives can be degraded by hydrolysis and bacterial activity. And, because the nature of the traces sampled

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Figure 4-32 Example of swabbing of a vehicle's dashboard using a commercial swab prewetted with isopropanol and water.

with the swab is most often not known, it is difficult to evaluate which is the best solvent to use with a swabbing system. Nevertheless, there is no general solvent that would suit perfectly all sorts of chemical traces. They all present some advantages and drawbacks. The material of the swab and the solvent, if any, should be chosen after careful consideration of the traces sought and the analytical techniques to be used later in the laboratory. Prewetted single-sealed swabs should minimize the possibility of contamination. CI Vacuum Lifting Vacuum lifting is generally preferred with fabrics. Particles are lifted by an air flow and trapped in a sampling device, generally a filter. It is important that the filter does not interfere with the compounds sampled. For example, drugs are generally vacuum lifted using a Teflon filter. Many on-site systems are equipped with a vacuuming apparatus. A disposable filter is inserted in the sampling unit of the on-site IMS apparatus, shown in Figure 4-31, before sampling (Figures 4-33 and 4-34). The sampling unit is then used inside the car (Figure 4-35). A specially equipped vacuum cleaner with disposable filters can also be used (Figure 4-36). Typically, vacuuming is performed just above the surface to be examined. When using a vacuuming unit, care must be taken to ensure that the components transferring the traces to the filter are absolutely clean. It is best to use disposable sampling units. If analytical instruments are available on-site, it is possible to perform a test before sampling to ensure that the sampling device is clean. A filter disk put into a disposable syringe barrel attached to a vacuum pump can be used as a sampling unit. The Forensic Science Laboratory of Northern Ireland developed an efficient vacuuming system for the recovery of organic and inorganic cartridge discharge residue [20, 21]. The suction sampling apparatus consists of a 25-millimeter diameter in-line Delrin filter holder and a 25-millimeter diameter Fluoropore membrane filter. Traces can be trapped on the filter using flexible plastic tubing and a vacuum pump (Figure 4-37). Several filter holders and filters are commercially available. Their dimensions and chemical composition can be chosen, based upon the desired sampling capability and the subsequent analytical steps. Larger holders and filters allow for

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Figure 4-33 A crime scene officer with personal protection equipment at the scene of a stolen-recovered vehicle prepared to perform a vacuum lifting of chemical traces in the vehicle.

Figure 4-34 The disposablefilteris inserted into the filter holder of the vacuuming apparatus.

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Figure 4-35 Vacuum lifting inside a car.

Figure 4-36 The specially equipped vacuum cleaner can also be used to vacuum lift samples of chemical traces inside a car.

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Figure 4-37 An expert sampling traces of explosives and gunshot residue using a Delrin filter holder, a Fluoropore membrane filter, a flexible tube, and a vacuum pump.

Figure 4-38 Tape lifting inside a car using small adhesive tabs.

larger samples to be collected. However, this can be problematic to extract and could yield larger amount of interfering material. Also, the material of the filters must be compatible with the solvents used in the extracting procedure. Dl Tape Lifting Collection of particles by adhesive tape lifting of surfaces is the favorite sampling approach for scanning electron microscope (SEM) analysis [8, 9]. The loss of stickiness restricts the size of area from which particles can be collected, and extraction procedures are more complex, due to the matrix effect of the adhesive. Figure 4-38 shows an example of tape lifting using a small adhesive tab performed on a fabric surface inside a car. Before sampling, it is necessary to plan not only the sampling technique, but also the number of samples to be collected. When properly used, several samples can provide topo-

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graphic data useful to gain information about the case, but too many samples can result in the loss of traces. A reasonable compromise for a car can be the choice of taking four samples from (1) the driver area, (2) the front passenger area, (3) the rear passenger side, and (4) the rear passenger driver side. One more sample could be taken from the space behind the rear seat and/or in the trunk. The information about the case should help develop the most appropriate strategy. For example, if an eyewitness sees a criminal hiding a pistol under the seats, samples should be taken from under the seats to verify this information. 4.11.6 Forensic Phase E: Packaging of Samples Samples must be preserved immediately to prevent any loss of materials and any risk of contamination. The packaging chosen depends on the nature of the trace. Volatile compounds (e.g., EGDN, NG, and TATP) may evaporate if the containers are not airtight. In this instance, clean metal cans or nylon bags specifically designed for that use are recommended. Also, small particles can be lost from packages that are not properly sealed. Proper sealing and packaging prevent the possible transfer of foreign matter from outside during transport and storage too. This is an important step in the contamination control procedure. Containers can be sealed with sealing tape and then with evidence tape signed by the collector. Several bags or cans specifically designed to collect evidence are commercially available. A reference to the sketch done at the beginning of the forensic activity can easily help to associate the sample to the area sampled, thus recording topographical information.

4.12 LABORATORY EXAMINATION OF SAMPLES 4.12.1 Analysis There are two levels of analysis for chemical traces that can be performed on samples: screening and confirmatory. Screening analyses are faster and cheaper than confirmatory analyses. However, screening analyses can give false-positive results and should solely be conducted to avoid more expensive and time-consuming analysis of negative samples. On-site analyses give only preliminary results that must be confirmed in the laboratory with more selective techniques. Traces of drugs are generally confirmed using GC or high-performance liquid chromatography (HPLC) with mass spectrometry detection [22, 23]. For the confirmation of organic explosives, both GC-CD and HPLC with electrochemical detection were often used in the past. Now HPLC-MS systems are more easily found in forensic laboratories. Ionic chromatography and capillary electrophoresis are used for the analysis of inorganic components in explosive substances [24, 25]. GSRs are generally analyzed using a scanning electron microscope equipped with an energy dispersive x-ray analyzer (SEM-EDX) that can isolate and help identify individual GSR particles through both morphological and elemental characteristics. An extended use of lead-free ammunition in the future could give more importance to other analytical techniques for organic GSR detection and identification [19].

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4.12.2 Interpretation of Results When interpreting analytical results in a forensic context, the probability of the evidence supporting a criminal activity (i.e., some explosive or drug was transported in a car) should be weighed against the probability of the evidence supporting alternative explanations [26, 27]. Currently, only limited data are available to assess the likelihood that a car might have become contaminated with drugs or explosives without being involved in criminal activities. The most important "population study" about explosive traces is probably the survey published in 1996 by Crowson et al., carried out to determine the background levels of explosive residues in public places [28]. Samples were taken from 25 taxis (124 samples) and 10 buses (87 samples) and NG was never detected, whereas RDX was found in 3 samples taken from taxis. Another group of samples was taken from 21 police vehicles (120 samples), and NG traces were found in 8 of the 21 police cars. Some tests simulating the transport of drugs or explosives in a vehicle can help rule out secondary or tertiary transfers and cross-contamination. Another aspect to consider during interpretation is the persistence of traces. During the investigation on the Mafia bombing attacks committed in Rome in 1993 (via Fauro, S. Giovanni in Laterano and S. Giorgio in Velabro), in Florence (via dei Georgofili, near the Uffizi Gallery), and in Milan (via Palestro), traces of the explosives used were found years later in the vehicles used to transport explosive and in places where explosive charges were prepared or hidden before the terrorist attacks. When interpreting evidence from GSR, it is necessary to understand that although chemical analysis can identify traces from the discharge of a cartridge, they cannot distinguish whether the traces were deposited on the surfaces surrounding the weapon while shooting or if they are due to a transfer from a surface rich with GSRs (firearm, cartridge case, bullet hole, etc.) to the hands or clothes of someone [8, 9]. Only by carrying out a topographical analysis of the traces it is possible to discriminate between different hypotheses (e.g., leaving a pistol under the seat of a car or shooting from inside the car). Thus, in case of GSRs, it is primordial for the exact location of the sampling to be carefully documented.

ACKNOWLEDGMENTS The author would like to thank the Institut de Police Scientifique, University of Lausanne (Switzerland), and RIS Carabinieri (It^ly) for providing some of the illustrations.

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