DNA Toolbox

DNA: One of Many Tools Used by Law Enforcement

DNA has shaped the investigative world forver

By: Evelyn Pence

DNA Only One Tool Used by Cold Case Investigators to Solve Crimes

Anyone who watches criminal investigation television shows is familiar with DNA as a crime-fighting tool. In 1987, Tommie Lee Andrews was the first person ever to be put in prison as a result of DNA (deoxyribonucleic acid) evidence. He was convicted of rape and ordered to spend 22 years behind bars.

This type of evidence was also a key factor in the arrest and subsequent conviction of Gary Ridgway, the “Green River Killer.” Ridgway pleaded guilty and was sentenced to 48 life sentences, to be served consecutively.

Viewers and the public have come to expect that DNA is part and parcel of an investigation. It is a valuable tool for investigators who are looking into cold cases, but it is only one part of the equation. The public can’t expect it to be something magical when the truth is that it is more like a match.

DNA Like a Match
A simple match can be used to make fire in the right conditions. It needs something to strike against, though, or it won’t work properly. DNA works in the same way in a cold case investigation.

If samples were taken at the crime scene, they sit until the investigators have something (or someone) to compare them to. This is not to say that the samples are useless or have no value, any more than the match cannot be used. It is merely waiting for the right circumstances to be lit.

Cold Case Investigators a Second Set of Eyes

Taking another look at the evidence or having a new investigator review the evidence that has been gathered to date can be a valuable exercise. Re-interviewing witnesses can bring new information to light and confirm their version of events. The “new” interview can be compared with the original one to see if the story is similar or if there are any discrepancies that warrant further questioning.

The inquiries may bring up facts that turn the investigation in a new direction. Some people will be eliminated as suspects, while others may not be able to be crossed off as easily. In the case of a murder or missing person investigation, a basic line of questioning will cover whether the person had life or business insurance and who stood to benefit from the relevant cover policy. No doubt the insurance company will want to see the case wrapped up as soon as possible since many of them will not pay out on a claim until it it is solved, but the police will need to do their due diligence to bring the matter to an appropriate conclusion.

DNA Not Helpful in All Cases

In the United States, DNA collected from a crime scene may be compared to samples on file with CODIS (“Combined DNA Index System”), the FBI’s National Index System. If a match is not found, the sample is run against a state database of convicted offender and arrestee profiles to look for one.

It’s possible that the person responsible for a crime is not in the system, which means that running the sample through CODIS or a similar system is a bit like looking for the proverbial needle in a haystack. This step is necessary to rule out a hit. Finding a match in a few seconds makes for a great television show, but it is probably not very realistic when it comes to solving cold cases in real life.

Grunt Work Still Necessary to Solve Crimes

The real work of solving these types of cases comes back to doing the “grunt” work of going through the evidence, talking to witnesses, and putting the pieces of the puzzle together. When a suspect is found that may be linked to the crime scene, then it’s time to strike the DNA match to see whether that person was present at the time.

If he or she was there, the evidence will support that fact. The case leading to that person as the perpetrator still needs to be built from the ground up the old fashioned way. That is not something that can be shown in a 60-minute television program, so it isn’t included. It does make for good, reliable police work, though. The case against someone has to stand up in court so that the guilty are convicted of their crimes.