DNA Analysis Isn't Foolproof, But One Pittsburgher Says It Could Be

Jul 11, 2017

The FBI has used the same protocols to process DNA for the last 20 years. It requires a human analyst to make comparisons based on subjective choices and simplified genetic samples.

Mark Perlin's product, True Allele, uses a different method. It's a program that lets computers process every high and low point in a piece of DNA – no comparisons or required.

On this episode of the Criminal Injustice podcast, host David Harris talks to Perlin about the program and how DNA analysis can be more powerful, faster and accurate.

Their conversation has been edited for length and clarity.

MARK PERLIN: What True Allele does is it explains the data. Unlike the human methods from the FBI, which discard data, it preserves the data, doesn't touch it and can try out hundreds of thousands of different ways of explaining the data. The better explanations have more probability, and they enter with higher probability into the final answer.

DAVID HARRIS: This comes up especially with crime scenes that have mixtures of different people's DNA. What kind of what kind of crimes would we see mixtures in?

PERLIN: You'd see mixtures in sexual assaults, where there's a victim and an assailant, or maybe a consensual partner. You'd see mixtures on almost any crime like a robbery where someone has touched a surface.

HARRIS: Touched a handgun, maybe?

PERLIN: Yes, and left their DNA on a handgun or a safe for a surface. And the DNA can be from four or five different people, so separating out who those contributors are before you would make a comparison is something the computer can do that people can't.

HARRIS: This came up in Allegheny County, here in Pittsburgh, in a case involving the murder of two sisters. Tell us about the Wolf sisters case.

PERLIN: In the Wolf sisters case, there was a lot of DNA evidence. The case was involved a lot of circumstantial evidence, because there were no eyewitnesses to how the two sisters were shot in their home. There were considerable DNA items. Most of them were mixtures and complex mixtures of two, three or four people, and in order to understand which of these suspects or victims were in items of evidence or not in items of evidence, a computer analysis was needed.

HARRIS: That's what you did in the Wolf sisters case, your software supplied that analysis, and that resulted in a guilty verdict.

PERLIN: Yes, based to a great extent on the ability of the computer to analyze DNA evidence.

HARRIS: Now if you could envision a world in which the cyber genetics method was in wide use, what would be the impact on the justice system?

PERLIN: First, we'd have information from all DNA evidence. The correct people would be convicted. The correct people would be exonerated. Most importantly, it would prevent crime.

HARRIS: How would it prevent crime?

PERLIN: For example, in the case of the Wolf sisters, there was a hat left by Allen Wade a month before the murders occurred. Using technology like True Allele would have detected that the burglar was Allen Wade. He would have been found on a real DNA database and apprehended, and these murders would never have occurred.

HARRIS: If somebody were to come to your company, a county's crime lab, and say, "We have all these untested samples. Can you help us?" What would your reaction be?

PERLIN: Our first reaction is and has been we will screen all of your evidence at no cost to help you determine where the information is in your current cases. And if you're interested, in your past cases. 

Criminal Injustice is an independent podcast recorded and produced in partnership with 90.5 WESA. Find more at criminalinjusticepodcast.com.