Forensic Chemistry/Trace Evidence Jen Pechal YAP 2010

Forensic Chemistry

What is Forensic Chemistry? Forensic chemistry is the use of chemical analysis as it applies to the law Differs from toxicology in that it analyzes non- biological samples instead of biological samples Accelerants, explosive residues and physical trace evidence Uses Chemical techniques to identify and quantify traces of known and unknown substances and trace their origins for the purposes of criminal investigations

Areas of Application Arson Explosives Trace Evidence Physical Match Accelerants Incendiary Devices Explosives Detonators, Powders Trace Evidence Powders, Drugs and Toxins Paint Fibers Glass Physical Match Soil, Lubricants, Cosmetics and Metals

Drug Testing Powders Liquids Tablets Capsules Vegetable material Non-drug powder

Drug Analysis Take notes describing the contents of the case heroin

Drug Analysis 2. Record the weight Determine misdemeanor or felony cocaine

Drug Analysis 3. Color test Marquis reagent chemical test for heroin (left); Cobalt thiocyanate reagent chemical test for cocaine (right)

Drug Analysis 4. Microscopic crystal test Gold chloride crystal test for cocaine viewed through crossed polarized filters next Sodium acetate crystal test for heroin viewed through crossed polarized filters

Drug Analysis Using a polarized light microscope

Gas Chromatography/Mass Spectrometry Separate chemical components from each other Identify each component

GC/MS Results Resulting Mass Spectrum of cocaine

GC/MS Results Resulting Mass Spectrum of heroin

Drug Analysis 5. Final report submitted to the agency and the District Attorney’s Office 6. Evidence is re-sealed 7. Store until the submitting agency picks it up

Arson Investigation During examination of a potential arson scene, cause and origin investigators collect debris they believe to contain accelerants

Arson Investigation Evidence is stored in airtight containers to avoid possible loss of the volatile components and is transported to the laboratory for analysis.

GC/MS Analysis Identify traces of ignitable liquid residue in these samples They accomplish this by adsorbing the accelerant residue onto activated charcoal strips. The concentrated accelerant is then eluted off the strip by dissolving in a solvent.

Gun Shot Residue When a firearm is discharged, gases are generated containing burned and unburned components from both the propellant and primer of the cartridge.

GSR Analysis End up on the Victim (clothing or skin) Hands of the person firing

GSR Analysis Scanning Electron Microscope (SEM) fitted with a energy dispersive spectrometer Scanning Electron Microscope (SEM) Energy Dispersive Spectrometer (EDS)

Gunshot primer residue particles as viewed on the SEM-EDS. GSR Analysis Tape lifts Presence of primer residue particles Gunshot primer residue particles as viewed on the SEM-EDS.

GSR Analysis Records the coordinates of the particle Barium, lead and antimony = primer residue

Noxious Chemicals Tear gas Capsaicin Commonly found in dye packs used by banks Capsaicin

Trace Evidence Powdered Substances Paint Transfer Fiber Analysis Glass Analysis

Trace Evidence Microscopic and macroscopic traces of physical evidence Found at various crime scenes Homicides Rapes Assaults Automobile accidents Hit and runs Burglaries

Trace Evidence Hairs Various hairs viewed through the stereomicroscope An animal hair viewed through the polarized light microscope

Fibers viewed through the stereomicroscope Trace Evidence Fibers Fibers viewed through the stereomicroscope A fabric impression in automotive paint

Automobile paint chips viewed under the stereomicroscope Trace Evidence Paint Automobile paint chips viewed under the stereomicroscope

Soil viewed through the stereomicroscope Trace Evidence Soil Add palynology Soil viewed through the stereomicroscope Pollen SEM

Polymer material viewed through the stereomicroscope Trace Evidence Polymers Polymer material viewed through the stereomicroscope

Glass viewed under the stereomicroscope Trace Evidence Glass Glass viewed under the stereomicroscope Glass fragments reconstructed to reveal bullet hole, illuminated with UV light

Trace Evidence Impressions A footwear impression in soil Footwear impression in snow prepared with snow print wax

Microscopic Trace Evidence Initial examination using a stereomicroscope The date on a dime viewed through a stereomicroscope Trace evidence viewed through a stereomicroscope

Microscopic Trace Evidence Synthetic fibers are analyzed using a polarized light microscope A fiber viewed through the polarized light microscope

Microscopic Trace Evidence Use a comparison microscope

Microscopic Trace Evidence More sophisticated chemical analysis on fibers and paints can be conducted using the micro-Fourier Transform Infrared Spectrometer.

Microscopic Trace Evidence If the fibers or paints are colored these can be spectrally compared on the Visible Microspectrophotometer.

Microscopic Trace Evidence Or if evidence beyond the capabilities of a normal microscope, the trace evidence section can utilize a state of the art digital Scanning Electron Microscope.  The fracture surface in Figure 9 shows evidence of ratchet marks and multiple crack initiation sites, indicating relatively high applied stresses

Microscopic Trace Evidence Solid materials: Paints Fibers Plastics are heated, broken down and volatilized Pyrolysis Gas Chromatograph- Mass Spectrometer A spectrum of an unknown sample

PGC-MS Results A comparison of two PGC-MS spectra