Science has revolutionized the way law enforcement officials are able to obtain a conviction against a suspect. If you are a big fan of the CSI TV shows and have noticed how those crime scene investigator (CSI) technicians collect evidence at crime scenes, then you would have seen those techs pick up minute pieces of evidence that could tell a story of what happened prior to their arrival.

Whenever a crime such as a sexual assault or a rape occurs, the perpetrator will leave something of himself at the crime scene. In particular, he will leave biological evidence that is ultimately collected by CSI technicians.

What happens if a perpetrator leaves only a tiny amount of evidence such as blood or semen? How can law enforcement be able to identify the culprit with such trace amounts? How can laboratory scientists step in to help get a conviction?

In 1993, a Nobel peace prize in chemistry was awarded to Dr. Kary B. Mullis for his invention of polymerase chain reaction (PCR). Dr. Mullis invented this technique while working for the Cetus Corporation in 1983. This method of replicating DNA, or copying DNA, is used to produce large amounts of DNA necessary for a DNA profile, another scientific procedure used to distinguish individuals of the same species using samples of their DNA.

In law enforcement, DNA profiling can be used to establish one person as the perpetrator or exclude another person as a suspect in a crime. This method has led to the exoneration of convicted felons who spent years behind bars while pleading their innocence.

In 1987, a Florida rapist, Tommie Lee Andrews, became the first person convicted as a result of DNA evidence used against him for the rape of a woman and burglary of her home. He was sentenced that same year to 22 years in prison.

Alternatively, in 1989, a Chicago man by the name of Gary Dotson was the first man to have his conviction overturned by using DNA profiling that excluded him as a suspect in a rape for which he was falsely imprisoned.

DNA profiling can also determine if there were multiple culprits involved in a crime such as a gang rape where one semen sample collected during a vaginal swab can yield more than one DNA sample.

Several jurisdictions now have databases that contain DNA profiles of suspects in a crime. In the UK, for example, the National DNA Database (NDNAD) contains well over 7 million records of as of 2007. NDNAD currently contains the most extensive DNA database in the world.

In the United States, the Combined DNA Index System (CODIS) contains the largest DNA database in North America. You have heard the mention of CODIS on CSI from time to time. CODIS is run by the FBI and helps solve crimes by searching DNA profiles sent in by federal, state, or local crime labs.

Science has been able to do more than just identify suspects in a recent crime. Some of these techniques have been used to establish a DNA profile on cold case crimes that occurred well before the invention of PCR. In fact, science has been able to establish DNA profiles from biological evidence extracted from known human remains in murder cases that occurred in the 60's.

Science has come a long way in helping authorities catch the culprits. Other than relying on witness testimony, juries have looked to scientific facts that have been able to speak louder on a witness stand in order to convince them to convict or acquit a defendant.

Gone are the days when witnesses falsely testify or poorly recall that a certain person committed a crime when he did not. Scientific evidence can make or break that case.

Today it is harder for a perpetrator to get away with a crime than it was 30, 40, or 50 years ago.