evidence. collection explosion usually followed by fire often destroyed by one or other dangerous...
TRANSCRIPT
Evidence
Collection
• Explosion usually followed by fire• Often destroyed by one or other• Dangerous – shards of glass or metal, toxic or
flammable vapors, 2nd explosion• Large crater = point of origin
• Collect soil and debris from inside crater• Test nearby objects for explosive residue or
pieces of detonator• Use sieves to sift for small pieces
• Follow chain of custody• Package separately in metal containers – label
where found
Analysis
• ID types of explosives & mechanisms of detonation
• First – preliminary tests, then confirmatory tests
• Use stereomicroscopy- examine debris for unexploded material- look for certain shapes and colors
- look for pieces of wrapper from dynamite, metal from pipe, pieces of wire
Chemical Analysis
• Wash debris w/ acetone to dissolve explosives• Color Spot Test – screens for various
explosives• Mix small amount of conc. acetone &
explosive solution with a specific reagent – observe
• Several tests –
• Several tests – - Modified Griess Test – presence of nitrite
(NO2-) (orange)- Alcoholic Potassium Hydroxide (KOH) –
presence of TNT (blue or violet)- Diephenylamine – most explosive
residues (not TNT or RDX) (blue or black)
Reactions
Explosive Modified Griess Test
Alcoholic KOH Diphenylamine
Nitrate None None Blue to Blue-Black
Nitrocellulose
Nitroglycerine
Trinitrotoluene (TNT)
RDX
PETN
Reactions
Explosive Modified Griess Test
Alcoholic KOH Diphenylamine
Nitrate None None Blue to Blue-Black
Nitrocellulose Orange None Blue-Black
Nitroglycerine
Trinitrotoluene (TNT)
RDX
PETN
Reactions
Explosive Modified Griess Test
Alcoholic KOH Diphenylamine
Nitrate None None Blue to Blue-Black
Nitrocellulose Orange None Blue-Black
Nitroglycerine Orange None Blue to Blue-Black
Trinitrotoluene (TNT)
RDX
PETN
Reactions
Explosive Modified Griess Test
Alcoholic KOH Diphenylamine
Nitrate None None Blue to Blue-Black
Nitrocellulose Orange None Blue-Black
Nitroglycerine Orange None Blue to Blue-Black
Trinitrotoluene (TNT) None Red to Violet None
RDX
PETN
Reactions
Explosive Modified Griess Test
Alcoholic KOH Diphenylamine
Nitrate None None Blue to Blue-Black
Nitrocellulose Orange None Blue-Black
Nitroglycerine Orange None Blue to Blue-Black
Trinitrotoluene (TNT) None Red to Violet None
RDX Orange None None
PETN
Reactions
Explosive Modified Griess Test
Alcoholic KOH Diphenylamine
Nitrate None None Blue to Blue-Black
Nitrocellulose Orange None Blue-Black
Nitroglycerine Orange None Blue to Blue-Black
Trinitrotoluene (TNT) None Red to Violet None
RDX Orange None None
PETN Orange None Blue
Chromatography
• TLC – Thin Layer Chromatography• Calculate Rf values• Use cellulose or silica gel plates as stationary
phase• Mixture of unknown explosives rinsed w/
solvent• Compared to knowns• Can also use HPLC
Confirmatory Tests
• After prelim ID• Infrared spectroscopy or Gas chrom – Mass
spec – confirm ID of organics (TNT, military explosives)
• IR spec – IR light passes thru sample and measures amount of energy it absorbs
• GC-MS – GC separates compounds in mixtureMS – compounds broken into smaller
charged particles – separated by mass & charge
Physical Evidence
• Clues about perpetrator• Pieces of wire, pipe, detonators – fingerprints,
explosive residue on clothes, serial number on watch, tool marks on pipe, torn edges of duct tape