cut and people said I looked so different.' Well, of course, your DNA is still the same, so those are things that are not written in your DNA. 

Why police turn to genetic genealogy in unsolved murder cases

Law enforcement, though, has another tool available: genetic genealogy.

It focuses not on telling them what a perpetrator might look like, but who they're related to.

That's the approach Arlington Police say ultimately helped them develop a significant lead in the case.

 It's all about these people who have their DNA in these genealogy databases that can help us out,  said Texas Rangers Lt. Jason Shea.

Shea wasn't involved in the Chavez murder investigation, but oversees his agency's use of genetic genealogy through a $1.5 million dollar grant from the US Department of Justice.

DNA phenotyping and genetic genealogy explained

The process, he explains, compares unidentified DNA to samples millions of Americans have shared with genealogy sites like FamilyTreeDNA or GEDmatch in an effort to learn more about their own family history.

In this approach, investigators can identify even distant families of a potential perpetrator.

 Let's say each one of us has 10,000 fifth-cousins. That's a lot of people. And do you even know who your second cousin is? Most likely not. So, we do get a lot of people who have some degree of separation in one of these databases,  said Shea.

Once investigators have found a family member of the person they're trying to identify, they may go knocking on doors and asking other relatives within the same family to provide DNA samples in order to work their way closer to a suspect.

With increased funding to cover its costs, the technology is playing a role in more cases.

 There are a lot of grants out there that are now expanding what they're allowed to be used for to include genetic genealogy because it's so powerful,  said Greytak.

The genealogy site, GEDMatch, is one that's embraced cooperation with law enforcement with its Genetic Witness Program.

According to its website, customers can  choose to opt in and enable law enforcement to solve violent crimes and exonerate the falsely accused. 

More than 2 million profiles, it says, are currently available through the program, and more than 1,000 cases have been solved as a result.

Greytak says genealogy sites limit what type of cases their databases can be used for.

 So, they say, they're only for unidentified remains and for violent crimes,  she said.  Also, these advanced DNA techniques are sort of considered last-ditch efforts. In some states, they're working on rules that every other avenue has to be exhausted before you can try this.