How DNA Technology Has Helped Solve Cold Cases

In order to identify unknown DNA and match it with other samples, DNA typically undergoes gel electrophoresis or another process.

In 2018, after over four decades of crime spree and investigation, Joseph DeAngelo, perhaps more famously known as the Golden State Killer, was finally arrested. In a most peculiar turn of events, it was information sent into a genealogy company, to which people can send in samples of their DNA to learn more about their ancestry and relatives, that finally identified him as the killer.

There has been a lot of advancement in the matching of hair, skin cells, and fingerprints to potential criminals, but the use of genealogy and other familiar information is a relatively new development. With this new technology, as was the case with the Golden State Killer, cracking cold cases becomes a much more achievable feat.

Gel Electrophoresis and DNA Matching

The DNA is extracted from a sample and is broken into fragments. The fragments then are put into wells, and the fragments of DNA slowly move down the gel, attracted by opposite electrical charges, with the largest fragments closer to the top, and the smaller ones near the bottom. Known DNA samples also undergo the gel electrophoresis, and when compared with the first unknown sample, can show the similarities in fragments, and consequently, traits.

For example, if there are two long fragments and one short fragment in the unknown sample, and there are the same numbers of these fragments in the same position in the known sample, you know those two samples are identical. This can be crucial when determining who left their DNA at a crime scene. But this method of DNA identification doesn’t always work because sometimes there is no known sample in any database to compare with the unknown sample.

So the next best thing is to find DNA that is similar to that left at the crime scene-similar DNA that often comes from family members.

Matching With Distant Relatives

When investigating genealogy leads on the Golden State Killer case, those working the case typically didn’t have any relatives closer to the culprit than third cousins. This means that the DNA that researchers were looking at was usually only less than one percent of a match to the DNA they already had from crime scenes. You share fifty percent of your DNA with each of your parents, and 25% with each of your grandparents, and as you continue to study more distant relatives, the matching genetic material gets smaller and smaller.

As all possible third cousins were found, they were added to a huge, quickly growing family tree that included any relatives that had any genetic similarities to the killer. Taking a closer look at the crimes and further evidence that came from them, investigators narrowed down the criminal based on physical characteristics like height, weight, and hair color, and by doing this, we’re able to narrow their genetic window, as well, eventually finding Joseph DeAngelo.

What the Future Holds

The discovery and arrest of the Golden State Killer have not been the only positive benefit from this new use of DNA on family trees. In Great Britain, for example, the DNA of a fourteen-year-old was found to be a close match to a murderer whose identity was unknown, and whose DNA could not be determined. The boy was too young to have committed the murder, but it was discovered that his uncle, in actuality, was the criminal.

Additional instances of success have happened in Los Angeles and Phoenix, and while there have been a lot of failures, with proper concern for privacy and more development in the accuracy of the matching, this use of genealogy and familial histories is very promising. It could even be used infamous cold cases, such as the murder of JonBenét Ramsey, and to provide closure for the victims and their families.

DNA has been collected and analyzed for a while now, but the use of family trees and ancestry websites is a recent, promising development. It has been successful in several instances, perhaps most notably in the capture of the Golden State Killer, and is sure to be continued in the future when faced with unknown DNA.