SerpApi.Org
The investigation into the 2012 murder of Irasema Chavez, which resulted in an arrest this week, highlights the evolution of DNA investigations.
It's one thing to have blood, semen or saliva and a potential suspect identified against whom to compare it. A DNA test, in that case, would simply be used to show whether it's a match or not.
It's a far more complicated investigation when law enforcement finds DNA and has no idea who it belongs to.
That's what happened in the Chavez case, when police found blood at the scene that wasn't hers.
How DNA phenotyping helped revive a 2012 Texas cold case
Four years later, in 2016, investigators sent it to a private company, Parabon Nanolabs, which was able to use phenotyping technology to figure out that the blood likely belonged to a woman with dark hair, dark eyes, and light brown to fair skin. They also created an image of what she might look like.
"Phenotyping is analyzing the parts of the DNA that actually code for the person, and so picking out information about their eye color, their hair color, their ancestry, the overall shape of their face, and we can put that all together into a composite image of that person," explained Ellen Greytak, Parabon Nanolabs' director of Bioinformatics.
The company's sketch drew renewed attention Monday after police announced the arrest of Mayra Velasquez, whose mugshot bore a striking similarity to the picture created a decade earlier.
Greytak says phenotyping can give police leads.
"In a lot of these cases, there's no witness. There's nothing for investigators to go on to narrow down, you know, among anyone in the world. And we're kind of coming in and saying, 'well, the DNA is there,' and the DNA can sort of serve as a genetic witness to at least give you some description of that person."
The approach, though, has its limitations.
"We can only know things that are written in the DNA, so things like age, you know, your DNA is the same the day you're born as the day you turn 80, so we can't pick that out," said Greytak. "Anything that's not genetic, tattoos, facial hair and you think, 'Oh I got a haircut 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."
