Forensic Arson Analysis

When detectives arrive at the scene of a fire, the first thing that they do is interview any witnesses to the fire, for example, the person who called the fire brigade and those who arrived before the fire department, whom may have seen how the fire began. When the fire has been controlled, the temperature falls, allowing the firefighters to make the building safe for investigation.  Similar to burglary and theft, arson is also a crime of stealth. The perpetrator of arson does not want to be seen committing his cowardly act. Most arson fires, therefore, occur at night and normally when no one is in the structure. Arson-for-profit is usually planned well ahead and the insured usually has a solid alibi far from the scene. 

 The investigation into how the fire started involves beginning at the lower levels, as fire travels upwards. The signs investigators search for when looking for the place the fire may have started include lingering heat, how deep the charring is, the flaking of building materials like cement and plaster, distorted plastic, metal and glass resulting from prolonged burning, damaged ceiling and structural damage.Samples are sealed in airtight containers and then tested for residues of accelerant liquid that might have been used to start the fire. These are the most common tests performed by forensics labs during an arson investigation:

• Static headspace heats the sample, causing the residue to separate out and vaporize into the top, or "headspace" of the container. That residue is then injected into a gas chromatograph, where it's broken apart to analyze its chemical structure.
• Passive headspace heats the sample and the residue collects onto a carbon strip in the container. Then the residue collected is injected into a gas chomatograph/mass spectrometer for analysis.
• Dynamic headspace bubbles liquid nitrogen gas through the sample and captures the residue onto an absorbent trap. The trapped compounds are then analyzed using gas chromatography.

References:

1. How Stuff Works
2. Fire Cops: On the Case with America's Arson Investigators
3. Fire Investigator Field Guide
4. Thinkquest team

Forensic Saliva Analysis

Body fluids, whether excreted or secreted, help our forensic experts compile detailed reports on sexual assaults, death, and the identification of attackers among other things.A forensic investigation can involve the analysis of body fluids, including saliva, for evidence of toxins and both prescription and illicit drugs.Saliva can be of forensic significance because traces of drugs that are circulating in the body can be present in saliva. The composition of the saliva accurately mirrors the proteins that are present in both the blood and the urine. Thus, testing of saliva, which is easier and less obtrusive than obtaining a blood or urine sample, can be used to reveal the presence of prescription and illicit drugs.

 Saliva is presented as an alternative matrix in the establishment of drug abuse. The ultimate salivary concentration is determined by the route of administration, the salivary pH, the degree of plasma protein binding,and the physico-chemical properties of the abused drug. Since the saliva/plasma ratio can exceed 1, saliva might be a better analytical tool than blood during roadside testing of potentially intoxicated drivers

 Virkler and Lednev add that Raman spectroscopy has great potential as just such a non-destructive tool. In 2008, the team reported that it could be used to identify bodily fluids at a crime scene but those experiments were carried out with just a single sample of each type of fluid. Now, the team has extended the work significantly to investigate the potential for spectroscopic differences among different "donors" of the same fluid.
The researchers have used near-infrared (NIR) Raman spectroscopy to obtain spectra for pure dried human saliva samples from several donors in a controlled laboratory environment. By applying principal component analysis (PCA) on the spectra they demonstrated that dry saliva is a particularly heterogeneous substance. However, the Raman spectra can be described as being a linear combination of a fluorescent background and three spectroscopic components.

New Forensics Tool Can Determine a Person's Age from a Spit Sample

Researchers at UCLA have figured out how to determine age to within five years from nothing more than a saliva sample.

The method relies on a process called methylation, which is a chemical change to one of the four building blocks of a person’s DNA. Methylation changes as our bodies grow older, contributing to age related diseases. In extracting DNA from saliva samples from more than 100 test subjects, the team found that it could zero in on a person’s age within five years by looking at just two of the 3 billion blocks that make up the human genome--such is the strong correlation between methylation and age.

 

References:

1. Enotes
2. Sourcebook in forensic serology, immunology, and biochemistry
3. Scientific Protocols for Forensic Examination of Clothing (Protocols in Forensic Science)
4. Forensic Biology: Identification and DNA Analysis of Biological Evidence