Journal of Forensic Science Society. — 1994. — April. — No. 2- P. 107-116.
Methodology for detecting traces of firearms and explosives |
The Journal of Forensic Science Society has published an article describing a method for detecting traces of firearms and explosives ( BB).
The above technique is an important aspect of the work of the forensic laboratory of Northern Ireland.
To detect such traces, forensic experts take swabs and very thin sections from the skin and surface of the suspect's clothing.
A set of forensic tools is used to take a swab. The specific method of taking a swab depends on what detection and identification methods will then be used in the lab.
Before a single set of tools was developed for these purposes, forensic scientists used two independent sets — one for detecting traces of gunshots and one for detecting explosives.
Therefore, some problems arose when it was necessary to simultaneously detect traces of firearms and explosives, since different methods are used to detect them. When examining clothing, those areas are usually examined that may contain traces of firearms and explosives.
As a rule, traces of firearms and explosives are located in different places; most often, these traces are incompatible for analysis.
Thus, if a forensic scientist takes a swab from a certain area of a suspect's skin to detect traces of firearm use, then a swab cannot be taken from that area of skin to detect traces of explosive use.
This problem has presented researchers with the task of developing joint methods for detecting traces of firearms and explosives and creating one universal set of tools that could simultaneously take swabs for different studies.
To detect traces of explosives, forensic scientists in Northern Ireland use gas and liquid chromatography methods, and to detect traces of gunshots, they use particle analysis.
The latter involves the detection and identification of particles left after a shot and individually inherent to a given type of firearm. Therefore, any sampling technique must be non-destructive.
When designing a set of sampling tools for the purpose of detecting traces of firearms and explosives, such circumstances as compatibility of the methods used with other laboratory forensic methods, as well as prevention of contamination of the samples collected with foreign substances were taken into account.
Factors such as ease of sample preparation, cost, chemical purity and availability of the materials used, the «life» time of the samples used, i.e. the time during which the samples taken are suitable for use, harmlessness to health and safety of the methods used were also taken into account.
The information obtained for the use of the methods used must meet the requirements for judicial evidence, i.e. so that this information can be presented in court as evidence.
In addition, the methods used should be such that the results of the studies could be verified and studied by other specialists who did not directly conduct the studies.
Taking the above into account, a set of tools and methods for detecting traces of firearms and explosives was developed.
Several police officers were trained in the use of this set. It was tested in practice. Only after that did they begin to mass-produce it, and it was recommended for everyday use in the work of criminologists and forensic experts.
The set of tools is placed in a nylon bag.
All instruments are packed in three separate hot-sealed polyethylene bags.
The first bag contains various instructions on how to use the set of instruments in certain cases, a sterile towel sealed in a damp foil bag and pre-irradiated with X-rays, and a ballpoint pen.
The second bag contains a large disposable suit and gloves made of a special synthetic material.
The forensic scientist wears them when taking samples and swabs. The coveralls are worn over clothing and shoes.
The third bag contains a hard plastic container with a lid, a spare container lid with a sealing device, a nylon bag, two tags including a police insignia tag, a sterile X-ray irradiated cloth, a standard crime scene report form, and tools and materials for taking samples and swabs.
As already mentioned, the toolkit contains comprehensive instructions on how to use them in various cases.
The room in which the examiner takes samples and swabs, as well as the examiner himself, must be absolutely clean and free of any contamination from traces of firearms shots and explosive residues.
Samples and swabs must be taken only with gloves.
Smears are usually taken from the hands, nails and face of the suspect.
Samples of hair from his head are also taken.
When examining clothing, samples are taken from both its surface and pockets.
To take smears, pieces of acrylic fiber soaked in 1.5 cm3 of isopropanol solution are used. These pieces of fiber are stored in polyethylene bags, packed and sealed in foil.
Smears are taken by smearing the area being studied several times. Then the sample is placed in a plastic tube-container with a lid, which is placed in a bag with a label, and this bag is sealed.
Acrylic fiber and a plastic tube are needed for subsequent forensic procedures.
Scrapings from the suspect's fingernails are taken with wooden sticks and then transferred to lint (a bandage material that has fallen into disuse: threads from it are plucked by hand from a cotton rag) and placed in a glass bottle.
When moving from one surface to another, gloves must be changed. All samples are placed in a container, which is closed with a lid and sealed with a stamp.
The container is placed in a nylon bag, which is labeled.
In addition to swabs and samples taken from the suspect, they are also taken from the suspected locations of shots fired (in cars and on the windows of houses from which the suspect is believed to have fired), from bullet holes, from places where bullets hit walls and obstacles, from suspected locations where weapons were stored, in cars that were believed to have been used to transport explosives, from places where explosives were concealed, from rooms used to manufacture and store bombs, and from places where explosions occurred.
Since swabs and samples are taken not only from the suspect but also from other locations listed above, a modernized general-purpose tool kit was created.
This was due to the fact that a tool kit for taking swabs from a suspect is quite expensive, but at the same time it is inconvenient for taking swabs and samples from other locations associated with the storage and use of firearms and explosives.
A general-purpose tool kit is suitable for crime scene examination. It also includes a disposable suit and gloves that the forensic scientist wears when examining a crime scene.
Some of the tool kits include hand sanitizers, while others do not.
The methods and materials used to collect samples and swabs from a crime scene are similar to those used to collect swabs and samples from a suspect.