Akshaya M, B.Sc. Forensic Science, RR Institute of Management Studies
A thorough collection of evidence include all the debris including sweeping from the
blast seen and the immediate surrounding area. Effective organization and composition
of the evidence processing team ensure the proper collection and preservation. Prior to
evidence collection the investigator would review the scene, identify the search
procedure for seen, brief the team and review assignments.
Identify, Collect, Preserve and Transport Evidence :
To maximize the recovery and evaluation and of all types of physical evidence, the
investigator ensure information such as item number, description, location found,
collectors name. The process involves assigning personnel to search areas, executing
scene – specific search pattern, determining bomb delivery methods, identifying
explosion site, documenting blast effects and examining victims. The investigation
involves in examining suspected bomb components, materials used in explosive
device construction and transport, carter materials, residues, trace evidence, weapons,
tools and comparison samples. Evidence identification, preservation and packaging
must be conducted safely, minimizing contamination and maintaining chain of
custody to establish possible crimes and ensure accurate investigation and prosecution
process.
Analysis of Explosive evidences :
The Analysis of Explosive evidence is in one of two forms :
❖ Analysis of pre blast or unexploded material – Bulk analysis
❖ Analysis of post blast or exploded material – Trace analysis
Systematic Procedure:
The Systematic procedure for both pre blast and post blast explosive evidence is
divided into four major steps:
❖ Preliminary Examination
❖ Extraction of Explosive material
❖ Detection of inorganic explosives including pyrotechnic composition
❖ Detection of oraganic explosives
Preliminary examination:
All outside packaging and seal condition is noted. The sample is tested for odour,
colour, consistency and visually observable ingredients, with odour detected
ingredients like mononitrotoulene, colour amd consistency guiding explosive type
identification, and visual contaminants.
Extraction of Explosive materials:
The solvent extraction of post blast debris is typical for extraction of explosive residues for further testing. Pre blast explosives are directly dissolved into the solvent
on the basis of solubility.
Four extracts are required for identification of unknown explosive material or residues.
1) Organic solvent extract
2) Water extract
3) Alkali extract
4) Pyridine extract
Organic solvent extraction:
Acetone is the universally accepted solvent for most organic explosives, while other
solvents like ether, benzene, and chloroform are used for specific groups. Extracts are
concentrated and tested for explosive detection and identification.
Water Extraction:
Acetone extract is treated with hot water, filtered, and concentrated. Chemical and
analytical tests detect water-soluble ingredients in explosive compositions like low,
inorganic, and pyrotechnic explosives.
Alkali extraction:
The residues left after water extraction often include metals, sulphides of arsenic and
antimony, sulphur carbon etc. A small portion of the dried material is extracted with
2N NaOH and filtered. The filtrate is preserved for the detection of sulphide, arsenic,
antimony, aluminum etc…,
Pyridine Extraction:
The residue left after the above extraction is dried and extracted with pyridine and
filtered. The extract is preserved for the detection of elemental Sulphur.
Conclusion:
A backpack left on a crowded city street. A gunman’s apartment. A meth lab in an
abandoned building. These are all areas where explosives have been found—ready to
detonate, endangering lives and property. In today’s law enforcement environment,
officers are more sensitive than ever to the possible existence of explosive devices.
The bomb squads who respond to these situations are highly trained to identify
explosives and to dispose, disrupt or render them safe. In a situation where an
explosion has occurred, investigators will scour the area to piece together clues to
help identify the type of device used and gather all available physical evidence or
witness testimony that could help lead to the bomber. Fragments of circuit boards,
fingerprints, even pieces of pet hair have been used to help narrow the investigation
and nab a perpetrator. Post-blast explosive residues can be analyzed using a variety of
techniques such as infrared spectroscopy, gas chromatography/mass spectrometry,
energy dispersive X-ray analysis, Raman spectroscopy and other techniques.
References:
❖ Alexander Beveridge.(1998). Forensic Investigation of explosions, Taylor and Francis Ltd,
Bristol.
❖ Yinon.J and Zitrin.S.(1981).The analysis of explosives, Pergamon press, New York.
❖ Yinon.J and Zitrin.S.(1993). Modern Methods and Application in Analysis of Explosives, John
Wiley and Sons, New York.
❖ Fritz Fiegl, (1965). Spot Tests in Inorganic Analysis, Elsevier Publishing Company, Amsterdam
❖ A.I Vogel,(1982) Text Book of Macro and Semi micro Qualitative Inorganic Analysis,5
thedition, Longman London
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