Over the last couple decades more and more police cases have been closed with the assistance of DNA testing evidence. From closing homicides, sexual assaults, robberies, and even more, police work has severely been amplified and improved with the introduction of this powerful scientific tool. More interestingly perhaps, certainly to those loved ones who have lost someone to a crime committed before this technology was commonplace, many cold cases- some as old as 50 years or more- are being resolved. While certainly any assistance DNA testing can provide for crimes being committed today is welcome news to law enforcement, the ability to go back in time and resolve cold cases is something most police officers ever thought science would be able to help them achieve.
How cold cases are closed
Cold cases, meaning police cases which have gone unsolved for a long period of time with no apprehension of the guilty party, are closed primarily when genetic testing is introduced into the investigation. Even police cases, especially those involving homicides that are more than 40 years old typically have a wealth of archived evidence. This evidence once reexamined using today’s testing technology becomes extremely powerful in associating a given suspect with a certain crime. For instance if a crime was committed in 1970 and there was evidence such as clothing of the victim, this material can now be combed for biological evidence. Evidence for testing can be found in many forms including blood, semen, hair strands, cigarette butts found at the scene of the crime and much more.
Once biological material is isolated from a sample, a DNA testing laboratory will sequence the genetic coding. This sequencing will produce a unique map identifying the person the sample was taken from in measurements of certain chromosomes. While the DNA test will not provide a name per se, it can provide a match.
Solving the crime
Due to limitations that most people are not already included in a readily available government database to compare their DNA coding, in most cases you need to have a suspect. Police detectives rarely cold case a file without a perpetrator in mind. In most cases prior to scientific testing, evidence was circumstantial. Police were in their minds sure they had the right person, only tying the suspect conclusively to the crime was oftentimes impossible without a witness. Now that DNA is available these cold cases can use the DNA on any items collected from the suspect during the investigation. In cases where the testing is not available using evidence collected from the crime scene, investigators can oftentimes secure warrants to test the suspect or even exhume a body in cases where the subject may have already been deceased.
Whatever the source, the collected DNA samples can be matched against one another for coincidences in genetic coding. If a suspect is tested and it results his genetic material was present on the body of victim of crime, the evidence is very strong and conclusive that the suspect can be now charged and convicted.
Testing can resolve missing person cases too
In addition to solving the crimes of today and yesterday, DNA testing has made available to ability to bring closure and comfort to grieving families of lost ones. Cases as far back as the 1930’s have successfully used DNA from exhumed bodies or remains against samples from living relatives. While in these cases due to some chromosomal mutation over generations the results cannot be 99.99% accurate as in a standard DNA test situation, the matches when found are usually overwhelming conclusive as to identification.