Forensic Aspects of Arson and Explosion Investigations Chapter

Forensic Aspects of Arson and Explosion Investigations Chapter 11

Forensic Aspects of Arson and Explosion Investigations • Complex, difficult, planned • Extensive destruction • Accidental causes: faulty wiring, electrical motors, heating systems, cigarettes • Training, knowledge, experience

Forensic Aspects of Arson and Explosion Investigations • On-site investigation • Motive, modus operandi, suspect • Detect, identify chemicals • Reconstruct, identify ignitors/ detonating mechanisms

The Chemistry of Fire • Oxidation- oxygen combining w/other substances to produce new substances • Energy- potential of a material or system to do work- heat, chemical, electrical, nuclear, light, mechanical • Fire- transformation process, oxidation produces heat and light (flame)

The Chemistry of Fire • Exothermic- chemical rxn that gives off heat, more energy is liberated than what is needed to break bonds • Combustion- oxidation w/ production of heat and light • Heat of combustion- the quantity of heat required to raise the temp of 1 lb of water 1 o. F, Btu- Table 11 -1 • Energy Barrier- energy requirement for initiation of reaction

The Chemistry of Fire • Ignition Temperature- minimum temp. at wh/a fuel will spontaneously ignite, heat energy input exceeds energy barrier, Table 11 -2 ex. Kerosene 410°F, Benzene 928°F • Speed of reaction- physical state and temp of fuel • Flame produced only when fuel in gaseous state (molecules colliding frequently) • Liquid Fuel- Flash point, lowest temp that vaporizes fuel (lower than ignition temp) • Solid Fuel- Pyrolysis, decomposition of solid organic matter by heat • Rate of rxn increases w/ increased temp

The Chemistry of Fire • Ignitors- match, electrical discharges, sparks, chemicals • Flammable Range: gas fuel-air mix, range that fuel concentrations in air are capable of burning • Ex- gasoline 1. 3 -6. 0% • Lean- fuel conc. too low • Rich- fuel conc. too high • Fire is “chain reaction”: fuel + air + energy heat burn heat ( cont. until oxygen or fuel runs out)

The Chemistry of Fire • Glowing Combustion (smoldering)burning at the fuel air interface w/o flames, combustion w/o pyrolization, after flames • Spontaneous Combustion- natural heat-producing process in presence of sufficient air and fuel, poorly ventilated area (bacteria, unsaturated oil soaked rags)

The Chemistry of Fire • Oxidizing Agents- chemicals th/supply oxygen for detonation • Ex- black powder (KNO 3, C, S) nitroglycerin (C, H, N, O)

The Chemistry of Fire • Three Requirements of Combustion: • 1) Fuel • 2) Sufficient oxygen (oxidizing agent) • 3) Initiation heat, heat to sustain rxn

Searching The Fire Scene • • • Immediate examination Safety, health conditions Search warrant not necessary Focus on finding fire’s origin Accelerant residue, containers Ignition device “Streamers” Breaking, entry, theft Eyewitnesses

Searching The Fire Scene • Probable origin- lowest point most intense burning ( fire moves upward) • Drafts, winds, collapsing structures, stairs, elevator shafts, holes • Accelerant flow to lowest point

Searching The Fire Scene • Protect located origin • Notes, sketches, photographs • Detect flammable liquid residues – “sniffer” (portable hydrocarbon detector), trained dogs • Fire Research Laboratory (Maryland)fire origin and cause, fire growth, spread, scene reconstruction

Collection and Preservation of Arson Evidence • Two- three quarts of soot and ash from fire’s point of origin • All porous materials, substances wh/may contain flammable residue (wood, flooring, rugs, rags, upholstery) • Airtight containers- (prevent evaporation), new paint containers, glass jars, leave air space

Collection and Preservation of Arson Evidence • Substrate Control- comparison of uncontaminated control specimens to suspect materials • Ignitors- matches, cigarette, firearms, ammunition, mechanical match striker, sparking device, “Molotav cocktail”

Collection and Preservation of Arson Evidence • Suspect’s clothing • Fluids in open bottles or cans collected and sealed • Soil, vegetation frozen to prevent bacterial degradation

Analysis of Flammable Residues • Gas Chromatograph most sensitive and reliable for detection and characterization of flammable residues • Hydrocarbons (gasoline, kerosene) produce characteristic chromatographic pattern (retention times) • Headspace (air space)- syringe • Vapor concentration (charcoal strip)inc concentration and sensitivity • Debris compared to standard

Analysis of Flammable Residues • Gas chromatography/Mass Spectrometry- separation and identification of mixtures

Science casts doubt on arson cases • Science Casts Doubt on Arson Convictions. doc

Types of Explosives • Homemade explosives and incendiary devices • Investigation by trained and experienced personnel • Bomb disposal, bomb-site investigation, forensic analysis, criminal investigation • Detect and identify explosive chemicals and detonating mechanisms

Types of Explosives • Explosion- combustion reaction proceeding at very rapid rate • Build-up of pressure from expanding gases • Blast effect (outward rush of gases) • Damage due to fragmentation debris and artificial gale

Types of Explosives • Classified according to speed at which explosives decompose • High Explosives(1000 - 8500 mps) • Low Explosives (< 1000 mps)

Low Explosives • Speed of Deflagration- very rapid oxidation, produces heat, light, low intensity subsonic pressure wave, slow burning rate • Propellant for ammunition or skyrockets • Fuel + oxidizing agent

Low Explosives • Black Powder- Potassium (sodium) nitrate (75%), carbon (charcoal) (15%), sulfur (10%) • Safety Fuse- black powder wrapped in casing • Confinement causes explosion

Low Explosives • Smokeless Powder- safest, most powerful low explosive • Single-base: nitrocellulose (nitrated cotton) • Double-base: nitrocellulose + nitroglycerin • Natural Gas + Air

High Explosives • Speed of detonation- extremely rapid oxidation reaction, supersonic shock wave, explosive charge, extremely sensitive

High Explosives- Primary Explosives • Ultrasensitive to heat, shock, friction, detonate violently w/o burning • Primers- detonate other explosives through chain rxn, explosive train • Blasting caps- lead azide, lead styphnate, diazodinitrophenol

High Explosives. Secondary Explosives • Insensitive to heat, shock, friction, burn when ignited, detonated by primary explosive • Dynamite, TNT (trinitrotoluene), PETN (pentaerythritol tetranitrate), RDX (cyclotrimethylenetrinitramine) and tetryl (2, 4, 6 trinitrophenylmethylnitramine)

High Explosives • Ammonium Nitrate-based explosives : • Water gels- water-resistant • Emulsions- oil and water phases • ANFO- aluminum nitrate soaked in fuel oil (Fertilizer + fuel oil)

High Explosives • TATP (triacetone triperoxide)homemade explosive used by terrorist organizations, friction and impact sensitive • Acetone, hydrogen peroxide, HCl acid

High Explosives- Military Explosives • RDX- most popular and powerful, composition C-4 • TNT- shells, bombs, grenades, demolition explosives, propellant • Military “dynamite”- TNT + RDX (does not contain NTG) • PETN- TNT mixtures for small caliber projectiles and grenades, commercially- explosive core of detonating cord (primacord) for simultaneous detonation

Collection and Analysis of Explosives • Collection of appropriate samples from scene • Crater at origin, material blown away • Undetonated residue of explosive, detonating mechanism • Collect soil, debris, porous and nonporous materials (wood, insulation, rubber, metal, etc. ) • Avoid contaminating scene (proper attire)

Collection of Explosives • Systematic search • Wire mesh sifters • IMS (ion mobility spectrometer)portable detection machinepreliminary ID of residues based on travel time due to size and structure

Collection of Explosives • Materials collected, packaged, labeled • Metal containers, plastic bags? • Separately

Analysis of Explosives 1 - Microscopic examination for unconsumed explosive (low explosives) 2 - Debris rinsed w/acetone (or water) to remove explosives 3 - Acetone extract concentrated analyzed

Analysis of Explosives. Acetone Extract • Color spot tests- Griess, Diphenylamine, Alcoholic KOH (Table 11 -3) • TLC • HPLC • GC/MS

Analysis of Explosives. Confirmatory Tests • IR Spectrophotometry-organic explosives (Ex- RDX) • X-ray diffraction -inorganic components of explosives (Ex- potassium nitrate, potassium sulfate)

Collection and Analysis of Explosives- Taggants • Proposed program • Tiny color-coded chips added to commercial explosives • Fluorescent and magnetic • Survive and recover from explosion • Trace and locate legal possessor • Switzerland

The World Trade Center Bombing (1993) • Urea nitrate bomb put into truck and driven into underground WTC garage and parked at 4 th level down • Subsequent explosion did extensive damage to several levels of the garage and less damage to other levels • Although goal was to topple WTC, little structural damage was done • Some loss of life

Goals of Investigation • Identify victims • Identify explosive • Recover bomb and timing device • Determine method of delivery

Evidence Sought • Investigators had to remove large quantities of concrete, steel and cars to get to bomb seat • Bomb seat contained most of the important evidence • Bomb parts; timer, casing, etc. • Explosive residue • Parts of truck that contained explosive

Areas of Forensic Science • • • Explosives Engineering Questioned documents Fingerprints Pathology DNA

The Murrah Building, Oklahoma City (1995) • ANFO explosive and timer packed into a rented truck, which was then parked outside Murrah building • Explosive confined to closed space such as truck is much more powerful • Resulting explosion resulted in severe damage to building and loss of more than 100 lives

Goals of Investigation • Identify victims • Identify explosive • Find timer and bomb parts • Determine method of delivery

Evidence Sought • Easier to find than in WTC because bomb seat outside building • Explosive residues • Bomb parts • Bodies and body parts; cadaver dogs, flies • Personal effects; helps in identification of human remains

Areas of Forensic Science • • • Anthropology DNA and serology Pathology Entomology Explosives Trace evidence Engineering Questioned documents Fingerprints

WTC Destruction (2001) • Large airplanes, loaded with fuel, crash into WTC buildings • Raging fires ignite everything in building above crash sites. • Metal supports melt from heat • Building collapses due to inability to support its own weight after structural damage • Thousands of people killed

Goals of Investigation • Cause known, no need to determine how destruction occurred • Recover and identify bodies, parts of bodies and charred remains • Recover personal effects that might help identify victims or perpetrators • Evidence that might determine how hijackings occurred.

Evidence Sought • Bodies and body parts; cadaver dogs, flies • Charred remains • Personal effects • Trace evidence such as charred papers • Weapons such as knives

Areas of Forensic Science • • • Anthropology DNA and serology Odontology Pathology Entomology Trace evidence Questioned documents Fingerprints Tools and toolmarks

TWA Flight 800 • • July 17, 1996 230 killed Calverton Explosive residue, pockmarks, tearing, “witness material” • Chemical analysis, GC/MS • Water soluble fuel?

Boston Marathon Bombing 2013 • • • 2 Pressure Cooker Bombs Explosives and Blasting Cap Electronic Device Initiator Shrapnel, Ball Bearings, Nails 3 Killed, 264 injured One suspect killed, one pled guilty

Mark Hoffmann. Salt Lake City • http: //investigation. discovery. co m/videos/solved-secrets-andbombs. html