The Bioscience Section of the Mississippi Crime Laboratory is the unit in which items of evidence are examined for body fluid stains. Biologists perform visual examinations of bulk items of evidence such as clothing or weapons to determine if blood or semen is present on the item. The locations of stains are documented, the stains are removed from the item; and if sufficient material is present, the stains are examined to determine if they are of human origin. Stains are then preserved for DNA testing. DNA testing is conducted on stains collected from the evidence as well as known reference samples to determine who contributed the stain. The type of DNA testing that is conducted is Polymerase Chain Reaction (PCR). During this technique, segments of the DNA molecule are copied numerous times so that about 1 billion copies of the DNA within a sample are made. This allows small stains or samples that are degraded to be tested. The goal of conducting DNA testing is to associate the crime scene stains with one of the individuals involved in the case.
There are three conclusions that can be reached when conducting DNA tests:
- an EXCLUSION opinion is issued when the genetic profile obtained from the evidence is not the same as the genetic profile obtained from a known reference sample. The person that the known reference sample was collected from is then excluded as the donor of the stain;
- an INCONCLUSIVE opinion is issued when, due to the quantity and/or the quality of the DNA within a stain, no information about the donor can be obtained and
- an INCLUSION opinion is issued when the genetic profile obtained from the evidence is the same as the genetic profile obtained from a known reference sample. The person that the known reference sample was collected from is then considered a possible donor of the stain. If an inclusion opinion is issued, a statistical number is reported that reflects the chance that someone unrelated to the person would have the same genetic profile.
The Bioscience Section also handles the blood samples collected from convicted offenders. Originally established to collect samples from sex offenders, the law was expanded to include all felons in FY 2003. Those individuals convicted of a felony must register with the Department of Public Safety per Section 45-33-01 of The Mississippi Code of 1972, Annotated. Part of this registration requires them to give a blood sample for DNA testing. Blood samples are collected at the time of registration, and these are forwarded to the Bioscience Section. DNA profiles are developed on these samples, and these DNA profiles are maintained in a database.
The database of DNA profiles developed from convicted offenders is the latest computer tool at law enforcement’s disposal. DNA profiles from casework stains can be stored in a separate database which can be searched against the convicted offender database. Serial cases can be linked together, and investigative leads can be provided in cases where traditional investigative measures have not identified the perpetrator.
In addition to searching DNA profiles within the state, DNA profiles can be searched across the United States through the FBI. The FBI will function as the national repository of convicted offender DNA profiles and casework profiles. Ultimately, each state’s convicted offender and casework databases will be searched against every other state’s.