Scientists believe that DNA serves as a blueprint for the visible characteristics of a person’s body. And that by studying the DNA of known people, they can predict the characteristics of an unknown person through their DNA.
That’s exactly what employees at Parabon NanoLabs are doing to help officers solve crimes.
The Chapel Hill Police Department turned to Parabon NanoLabs in 2016 after working for four years attempting to figure out who killed 19-year-old Faith Hedgepeth in a bedroom at her shared apartment near the UNC-Chapel Hill campus.
Ellen Greytak, director of Bioinformatics and the technical lead for the Snapshot Advanced DNA Analysis division of Parabon NanoLabs, said the company uses DNA from crime scenes to create a composite sketch of the killer.
“We look at DNA like a blueprint,” Greytak said.
Her staff picked apart the DNA found at Hedgepeth’s crime scene.
Their analysis came back with the following description of possible suspect physical characteristics.
▪ Black hair.
▪ Olive skin.
▪ Hazel eyes.
▪ Few, if any, freckles.
The analysis appeared spot-on when officers arrested 28-year-old Miguel Salguero-Olivares last month on a first-degree murder charge in Hedgepeth’s death.
But how did the scientists get there?
“There’s always variables, but the way that we make our prediction is a probabilistic prediction,” Greytak said.
Testing known characteristics
Greytak said Parabon NanoLabs looks for five eye colors: hazel, brown, blue, green and black.
She said the lab compares the DNA of 1,000 people with these characteristics to the DNA of an unknown suspect.
That gives them the probability of the suspect’s eye color based on their known samples.
They do the same for skin tones, hair color, face shape and whether freckles are present.
When they give their prediction to the police, they include a percent-confidence interval for each characteristic.
“We can never be 100% sure, because we haven’t seen every person in the world,” Greytak said.
The lab provides the probable characteristics to an artist, who creates a composite sketch of the suspect.
Greytak added that facial characteristics include whether the suspect might have a wide jaw, a high-set nose or narrow eyes. But she said things like earlobe attachment or which hand is dominant are more complex and harder to predict.
She also said that the DNA a person is born with is the same as when they die. Age, weight and hairstyles can’t be determined through phenotyping.
Often when the artist creates a composite for police, the drawing is done as if the suspect were 25.
“They’re always going to have the same face, same eye color and same skin color, and so all of that is written into your DNA,” Greytak said. “It’s just a matter of finding it.”
She said she stresses to police that the drawing and predictions are just that and not to be used without other evidence.
Greytak said that of the 181 cases Parabon NanoLabs is credited with helping to solve, a little more than a dozen were solved using just phenotyping.
“This is definitely a much smaller number,” Greytak said.
Other cases were solved through genetic genealogy, which matches DNA from a crime scene to DNA uploaded into a public database. From there a genealogist works the suspect’s family tree backward until she can figure out who the DNA belongs to.
“The phenotyping is just — it’s a lot less specific than genetic genealogy, but what we found is that it’s really useful to use with genetic genealogy,” Greytak said.