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DNA Evidence
In 1987, the first American was convicted using DNA evidence. Tommie Lee Andrews was convicted of rape, aggravated burglary, and burglary in Florida and sentenced to twenty-two years in prison after he broke into a woman’s home and raped the woman at knife-point. Forensic scientists were able to match DNA from Andrews’s blood and the samples of semen from the crime scene. This conviction eventually led to a DNA database for each state.
A database has been set up similar to the fingerprint database, AFIS. The database contains DNA of convicted offenders, unsolved crime scene evidence and missing persons. The database is called CODISCombined DNA Index System. If there are no suspects in a crime, investigators will enter the analyzed crime scene DNA into CODIS to see if there is a possible match. There are three tiers to CODIS – local, state, and national. For the CODIS database, the FBI uses 13 standard regions of nuclear DNA called Short Tandem Repeats (STR) that vary among individuals. STR’s are small sections of DNA that differ in how many times the base sequences (A, T, C, and G) repeat among individuals. STR analysis is currently the most commonly used DNA profiling technique used in forensic science. Remember that in Lesson 5.01, you learned that each person’s DNA differs by 0.1%. These 13 regions are known areas that individuals are unique. One of the 13 regions matching between two DNA samples is not rare, but four or five matching regions most likely indicate a match.
Even though DNA analysis is relatively new to the field of forensic science, there have been plenty of cases where DNA evidence has been a key piece of evidence. Cold casescases closed and reopened from the past use DNA evidence often to help solve cases. Most cold cases didn’t have the DNA technology we have available today when they were first opened.
