Identification

• DNA evidence can be used for many purposes, one of which is evidence in arson cases. DNA samples present a unique pattern for every individual, much like a fingerprint. Because everyone's DNA is unique, DNA can be harvested from any area where cells from a person have been left behind. Cells are commonly attached to skin cells and hair follicles that have fallen out.
  
  

Features

• DNA evidence can be generated by comparing DNA left at a scene with a sample from a suspect. While DNA can can come from any type of cellular material left behind at the scene, the suspect's control sample must be more carefully obtained. Contaminated or tainted control samples can be challenged in a court of law. The best samples are obtained from a cheek swab, or though blood, saliva or semen.
  
  

Considerations

• The first DNA testing for arson cases involves restriction enzyme digestion. Restriction enzymes are proteins that chop up DNA based on particular patterns. As a result, different individuals have different lengths of digested DNA. These sections of DNA can then be separated based on size. This technique, however, requires a large amount of DNA to be analyzed and can be hard to interpret.
  
  

Function

• A more modern type of DNA analysis for arson cases utilizes short tandem repeats. Short tandem repeats are small regions of DNA that can be found throughout the person's DNA. Because every individual has different numbers and locations of specific short tandem repeats, these sequences can be used to generate a genomic fingerprint. Analysis of many different areas of these repeats can allow for successful matching of an individual to tissue left behind at an arson crime scene.
  
  

Warning

• DNA evidence has often been misrepresented by defense lawyers. In these cases, the statistics regarding DNA evidence are misrepresented to make it seem as if the evidence could come from a number of people. Using the best DNA analysis procedures, the likelihood of a match occurring via coincidence is close to 1 to 100 billion. However, in actual practice, the risk of an error being made is greater, due to mistakes and faults within laboratory equipment and technicians.