Transcript document
Arson and Explosives Using Forensic Chemistry to Identify Substances Arson – Incendiary Fires • Accelerant – something used to promote and spread a fire – Solid accelerants include paper, trash, highway flares, black powder, paraffin and an oxidizer, or sugar and chlorate. – Liquid accelerants include petroleum products, alcohols, paint thinners, industrial solvents, and ether. Either “sloshed about” or used in firebomb (Molotov cocktail). – Gaseous accelerants include propane and natural gas (disconnected gas line) Incendiary Device • Combine a means of ignition with a time delay. – Candle is allowed to burn down to come into contact with accelerant. – Fuses, flares, matches with lit cigarette, chemical mixes, electronic devices. Collection of Potential Evidence • Use clean, vapor-tight containers. – Screw-cap glass jars, metal cans, unused paint cans with tight-fitting lids • Care must be taken to avoid loss of evidence due to evaporation, and to avoid cross-contamination of exhibits Search for Evidence • Some materials will survive the fire • Start at point of origin (determined by arson investigator) – Wires, batteries, bottles, wax, soap (used to “gel” flammable liquid), ash residues, unburned residual liquids Testing Evidence • Gas Chromatography – Heat airtight container to drive volatile residues from collected evidence – Remove vapor with syringe and inject into GC – Unburned liquids can be removed from evidence by steam distillation, vacuum distillation, solvent extraction, solvent rinsing, or air flushing. – Compare resulting chromatogram with those of known substances Explosives • 1920s - dynamite bombs used by political anarchists aimed at rich and powerful, also used by unions • 1930s – the mob used stink bombs in theaters and restaurants to “persuade” them to sell • November 1, 1955 – midair explosion of United Airlines flight 629 – first bomb aimed at “general public” Bomb Investigations • Investigation of flight 629 was very similar to how such investigations are carried out today • Large grid was established (pieces were scattered over a 5-mile radius) • Wreckage was pieced together, and it was determined what type of bomb was used (from residues) and where it exploded Types of Explosives • Low explosives – cause relatively small damage – Explode at a few thousand feet per second – Emit low frequency sound (puff or boom) – Examples are gasoline and gunpowder • High explosives – cause large damage – 25,000 feet per second – High-frequency blast – Examples are dynamite and nitroglycerin • Military Explosives – TNT (trinitrotoluene), RDX, PETN (Pentaerythritol Tetranitrate C5H8N4O12) • Commercial Explosives – black powder, ANFO (ammonium nitrate-fuel oil), dynamite, nitrostarch • Improvised Explosives – usually low explosives (require confinement) – homemade black powder, fuel mixed with an oxidizer. Crime Scene Searches • Focus on blast seat • Diligent search for remnants must be performed – Explosive residues, metal fragments, fuse or blasting cap, wire and/or insulation, electrical tape, batteries, clocks or timers • FBI has extensive databases (batteries, detonators, accessories, timers, radiocontrol devices Laboratory Tests • Microscope – locate unconsumed explosive • Acetone is used to extract soluble explosives from debris – TLC or HPLC • Evidence is screened with an “explosives detector” – a special GC that identifies known explosives.