lady testing dna

This year Portland police announced that they solved a 40-year-old local murder case. How did they do that? With the help of an ancestry test.

Detectives matched crime-scene DNA to data posted on a public genealogy site. This helped them identify a man who assaulted and strangled a 20-year Anna Marie Hlavka on July 24, 1979. The murderer turned out to be Jerry Walter McFadden, a serial killer from Texas.

Last year California authorities used the same technology to identify and arrest the Golden State Killer, Joseph James DeAngelo. Their example inspired the Portland detectives to try the same method for identifying Hlavka’s killer — and it worked!

However, how exactly does it work?

Genetic Genealogy Technique

Genetic genealogy is a new investigative technique which is basically a blend of DNA analysis and traditional genealogical methods. Sounds too difficult? Let’s explain it a bit more.

The investigators have been using DNA matching techniques in their work for the past few decades already. Such techniques look simple: all you need to do is to take a DNA sample at a crime scene and run it through a database to match with a suspect’s DNA. However, such samples don’t always match, and when they don’t, the DNA cannot tell you much more.

At least, it couldn’t before. Nowadays we have all these open-access genetic genealogy databases that help investigators in their work. If an investigator uploads a genetic data collected at a crime scene into such database and runs a comparison, they often find what they’re looking for.

How Genetic Genealogy Databases Work

Such databases (like GEDmatch and many similar ones) initially were created to help people learn more about their ancestors. They are very easy to use: people take a consumer genetic test and upload the results to such a database. They also decide how much personal information do they want to attach to these results (and do they want to attach such information at all).

After the upload is complete, the database’s search tool compares this data to the other uploaded to a database to find out if there are some similarities with other users. It worth noting that not every similarity counts: the search tool takes the percentage of shared DNA into account to ensure that the people are related and a match isn’t accidental.

Close relatives share more DNA: half of the genes if they are siblings, an eighth if they are first cousins. Such tests can identify relatives starting with great-great-great grandparents and ending with third cousins: past this line, people share so little DNA that it’s hard to tell whether they are related or not.

Using Genetic Genealogy in Crime Solving

Let’s assume that an investigator runs a DNA sample through such a database and finds a match. What happens next?

Actually, that’s where the hard work starts. It isn’t enough to merely find a match when you’re working on a cold case: you need to build an extensive family tree to identify the criminal. So once the results are in, a genealogist starts digging through archives, birth records, and even social media to build up that tree based on a common ancestor.

Once the work is done, the researches have to follow the branches of that tree starting from the beginning and ending with the present day. Their goal is to identify the person who was living or traveling in the area where the crime happened. They also have to make sure that the age and physical characteristics of that person match the suspect’s description.

This doesn’t merely look time-consuming — it’s in fact is. However, it’s indeed effective: such a technique already helped solve more than 30 cases that would be hardly possible to solve otherwise.

Privacy Issues and Other Challenges

Despite the effectiveness of this technology, it isn’t widely appreciated and approved. Many people see it as a violation of their privacy and feel uneasy about how their genetic data might be used. That’s why many genetic testing companies have signed on to privacy best practices: they are transparent about the number of law enforcement requests they get and agree to.

Furthermore, people react differently to the circumstances of database usage. According to last year’s survey, most people are supportive when the data is used in police investigations. However, they show such support only when the searches are related to cases with violent offenses; the support diminishes if it’s nonviolent cases we’re talking about.

Without a doubt, genetic genealogy technique can do wonders for the police system and the crime-solving in general. It already does wonders for cold cases that otherwise would have little chances of being solved. Hopefully, the public support of this technology will also increase with time.