Forensic Genealogy Solves the Golden Killer Cold Case

Today on CS-Science we are talking about DNA and the emerging field of ‘forensic genealogy’, a new field which is really changing how police solve crimes.

In the 1970s and 80s the Golden State Killer terrorised California, being responsible for 100s of burglaries, as well as rapes and a dozen murders. And they never found who did it. That is until last year when they finally caught him using forensic genealogy.

Forensic genealogy uses DNA technology, so let’s talk a bit about that first.

DNA was first used by forensic scientists in the 1980s, and since then it has had a huge impact on how they solve crimes. And we all know what this looks like, we see it on TV all the time.

You heard her. DNA analysis, or DNA fingerprinting is the ‘perfectly accurate test’ used get a match between blood, skin, saliva found at a crime scene and a suspect. In that NCIS episode, Abby said they got DNA from a hair… let’s give them the benefit of the doubt and say it had a root attached… because that’s the only way to extract DNA from hair!

But DNA analysis is highly accurate, it can tell the difference between my spit and your spit. But Abby, our NCIS forensic analyst also said DNA from a tree is very similar to human DNA. Is this true? To answer that, we have to ask the question…

It is a very good question!

DNA stands for DeoxyriboNucleic Acid. It is a molecule that forms two chains that coil around each other to make what we call the Double Helix.

 It contains all the genetic instructions that makes you, you. Or me, me.

Or a tree a tree? While Abby is right that DNA is in all living things, and it is the same sort of DNA in trees and human (there is only one!), there is no chance of falsely accusing a banana of murder.

This is because DNA fingerprinting looks at the differences in DNA between people. And even though all humans share 99.9% of their DNA, that different 0.1% is enough to tell us all apart.

Forensic scientists look the types and sequences of proteins in our DNA, represented here as a kind of barcode. Here we have a theoretical DNA profile from a crime scene compared to the DNA profiles of three suspects. It looks like Suspect #2 might be in some trouble!

Until recently, unless you had a suspect’s DNA it was not possible to get a match to a crime scene. A suspect’s DNA might be in the database if they had already committed a crime, police could ask a suspect for a sample, or get a sample by more sneaky methods…

But now that has changed. More and more people choosing to get DNA tests through websites like Ancestry.com and 23andme, to find out about their heritage and find distant relatives.

A lot of people are spitting! But long lost relatives are not the only ones using this information. Police are using these DNA databases solve crimes, including the case of the Golden State Killer, a case that had been cold for 40 years!

Police had a frozen DNA sample from the Golden State Killer’s crime scenes. They thawed it out, analysed it, and uploaded the results to GEDMatch, a website where you can use your DNA test results to find your relatives.

It was NOT a match! The Golden State Killer had not uploaded his own DNA to the site.

But, the site did identify some people that were distant cousins of the killer.

Using some old fashioned genealogy methods, like looking at marriage and birth records, they were able to construct a family tree and identify who the killer might be.

Let’s use the Simpsons’ family tree as an example. Let’s say Homer steals a donut and leaves his DNA evidence on some donut crumbs recovered from the crime scene. Years later, his distant cousin David Bernstein wonders about his ancestry, does a spit test, and uploads his results to GED match.

Police know that Homer’s DNA is similar to David’s, so they are probably related. Once they have constructed a family tree they have a list of suspects, that is people who are related to David. Some are too old, (or dead), others are too young to have committed the crime years before. They know it’s a male from the DNA, so any female suspects are ruled out.

This leaves them with a shortlist of possible donut thieves to focus all their investigative efforts on.

And this is how police finally caught up with the Golden State Killer, identified as Joseph James DeAngelo, now and a retired policeman. He was arrested in April 2018 and is awaiting trial.

This case revolutionised how DNA can be used to solve crimes, and many other cold cases and now being revisited.

That’s all from CS-Science today! See you next time!