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Home > Criminal Investigation & Forensics > Crime Lab > Lab Services > Forensic Chemistry/Trace evidence

Forensic Chemistry

The physical contact between a suspect and a victim, vehicle or a crime scene during the commission of a crime, can and often does result in the transfer of materials such as blood, semen, saliva, hairs, fibers, paint, plastic and adhesives. Also, in the investigation of fires, the analysis of fire debris samples for the identification of ignitable liquids is necessary to help determine the cause and origin of the fire. The Forensic Chemistry Section of the Crime Laboratory is responsible for the examination, identification and/or comparison of these types of materials which may be present at the crime scene, on the victim, the suspect, clothing articles, vehicles, weapons, tools and other objects. In order to conduct these examinations, various serological, chemical, microscopic, and/or instrumental techniques are utilized.

Serology

In homicide, sexual assault, aggravated assault, motor vehicle accident, burglary and other investigations, the Forensic Chemists routinely conduct serological examinations on clothing articles, weapons, vehicles, scene samples or other items in order to locate possible bloodstains, identify the blood by presumptive chemical testing, determine if the blood is of human origin and then select suitable and relevant samples for DNA analysis. The chemists also make observations of bloodstain patterns on evidence items and/or at crime scenes. When evidence is submitted in sexual assault cases, the Forensic Chemists examine the contents of sexual assault evidence kits, clothing articles, bedding or other items for the presence of semen. Possible semen stains are located visually or by alternate light source and then tested for a component of seminal fluid by presumptive chemical tests. Further testing is conducted microscopically for sperm cells. In the absence of sperm cells, further testing is carried out for an additional semen component in order to confirm the presence of seminal fluid. Suitable and relevant samples are then selected for DNA analysis. In some instances, saliva analysis is also requested. Stains are generally located visually or by alternate light source. Amylase, a chemical component of saliva, is identified to confirm the presence of saliva. Suitable and relevant samples are then selected for DNA analysis.

Bloodstain Pattern Analysis

Bloodstain pattern analysis involves the examination and documentation of bloodstains, namely their size, shape and distribution. Bloodstain patterns are often indicative of the types of actions that produced or caused these patterns. This information is used to help reconstruct the sequence of events that occurred during the commission of a crime.

Biological screening Blood spatter measurements

Trace Evidence

Trace evidence includes materials that are often microscopic in size and are easily transferred between victims, suspects, clothing articles, vehicles, weapons, tools and other objects. These types of materials mainly include paint, hair, fibers, plastics and adhesives (tape). Also encountered are fabrics, fabric impressions, cosmetics, gunshot residue particles and ropes and cordage. These types of materials which may be found and collected during investigations are compared to known or reference samples using various chemical, microscopic and instrumental techniques. The types of microscopes used include the stereomicroscope, the compound microscope, the comparison microscope and the polarized light microscope. Instruments used include the Fourier Transform Infrared Spectrophotometer (FTIR) and the microspectrophotometer (MSP). The Forensic Chemistry Section participates in the Paint Debris Query (PDQ) system, sponsored by the Royal Canadian Mounted Police (RCMP) and Federal Bureau of Investigation (FBI). The PDQ database allows an examiner to process an automotive paint chip and potentially determine the make, model, and year of a vehicle. The PDQ database is especially important in difficult cases where investigators do not have a clear suspect vehicle.

Fire Debris Analysis

The Fire Debris Analysis Unit examines evidence collected at fire scenes and is a part of the Forensic Chemistry Section of the laboratory. The purpose of this examination is to determine if an ignitable liquid is present. Most ignitable liquids are petroleum products, however other non-petroleum products can be identified. Fire debris evidence is packaged in mason jars, paint cans, or fire debris evidence bags and generally consists of charred fire debris or clothing items. The examination procedure involves extracting ignitable liquids from the evidence using one of three extraction techniques or a combination of techniques. The three extraction methods used by this laboratory are Passive Diffusion Headspace, Simple Headspace, and Solvent Extraction. The extract is then analyzed on a Gas Chromatograph Mass Spectrometer, which provides data that the examiner will then analyze. Based on the pattern, or appearance of the data, the examiner will identify the type of product, if any, in the extract.

Note: Additional information pertaining to the examination of Serology Evidence, Bloodstain Patterns, Trace Evidence and Fire Debris Evidence may be found in Forensic Science related texts by Richard Saferstein, Henry C. Lee, Robert Gaensslen, Barry A.J. Fisher, Ross Gardner, Thomas Bevel and others.