Investigating Sexual Assault, Essay Example

In sexual assault cases, investigators should collect a number of samples after a suspected sexual assault. These include blood and urine samples to test for evidence of drug-facilitated assault, as well as DNA samples from the victim and the suspected perpetrator. A variety of other forensic evidence can be useful, such as the collection of blood, hair, or other samples from the scene. The primary concern is to collect as many types of biological and forensic evidence as possible.

Investigators use a database called CODIS, the Combined DNA Index System, to maintain and compare DNA samples from convicted criminals and potential criminal suspects. The samples in CODIS cannot be used as evidence in court proceedings, but they may help investigators identify a perpetrator by comparing evidence from a crime scene to the information in the database. CODIS maintains DNA information from state databases of convicted offenders and arrestees profiles (in the states where DNA can be collected from arrestees).

PCR stands for polymerase chain reaction, and is a process used to duplicate DNA samples to make them usable for DNA testing.  STR stands for short tandem repeats, which are “microsatellites” of DNA. PCR/STR testing is a process allows investigators to duplicate and amplify small or degraded DNA samples in order to make them suitable for testing.

Mitochondrial DNA, or mtDNA is found in the mitochondria, which are small structures outside the nucleus. While DNA can only be found in the nucleus, and in relatively small amounts, mtDNA is present in much larger amounts in the cell structure.  mtDNA is passed along to offspring from the mother, while only regular DNA is passed along from the father. Because mtDNA is passed along only from the mother, it is an exact copy from one generation to the next

DNA is present in only two copies per cell. mtDNA is present in hundreds of thousands of copies per cell, making it much easier to find. This can be useful in cold cases or other cases where DNA samples are difficult to acquire. It has also been useful in doing DNA testing on hair samples. When hair samples do not contain the root, it is impossible to get DNA for testing, but mtDNA is present in large amounts in hair. Recent advances in using mtDNA for testing have made it easier for investigators to use it in criminal and forensic investigations.

References

http://www.fbi.gov/about-us/lab/codis/codis-and-ndis-fact-sheet

http://www.forensicmag.com/article/dna-forensics-rflp-pcr-str-and-beyond?page=0,1

http://www.pbs.org/wgbh/nova/neanderthals/mtdna.html

http://www.safeta.org/displaycommon.cfm?an=1&subarticlenbr=188