"And what's wrong with that?" Stahl asks.
"Because it's not a partial plate. We're talking about DNA. DNA is different. DNA contains a vast amount of intensely personal information," Mercer says.
And he says there are serious racial implications, because since blacks are overrepresented in the prisons, and therefore in the DNA database, extending it to relatives would magnify the disparity.
"What you're gonna end up seeing is nearly the majority of the African American population being under genetic surveillance," Mercer says. "If you do the math, that's where you end up."
"Extremely specific question. You have a crime lab looking at DNA in a horrific crime. They get a partial match, a very close match, and the DNA expert suspects a brother. Should he withhold that information from the police, or should he tell the police, 'We think a brother did this?'" Stahl asks Mercer.
"If it comes from a database search?" Mercer asks.
"Yes," she replies.
"Then it should not be revealed," Mercer says.
"So, the DNA expert should just say, 'Sorry. No match.' And that's the end of it? And not pass this incredible clue along?" Stahl asks.
"That's correct," Mercer argues.
Mitch Morrissey says he has a big problem with that. "They have this information. And they're not telling the lead investigators? How do they justify that to the next victim of this serial rapist?" he asks.
Morrissey thinks the U.S. should do what the British are doing: they have developed a technique to scour their DNA database, deliberately searching for partial matches that might indicate a relative.
It's called "familial searching," and the city of Rotherham used it to try and catch a criminal who had eluded police for 20 years. Back in the 1980s he was called the "shoe rapist," because of the pattern of his attacks.
"It was a lone female walking home. Invariably they were wearing stiletto shoes. They were tied up using stockings, and their shoes were always stolen," explains Det. Sue Hickman.
Hickman was given a list of 43 people in the area who could have been related to the rapist. The third door she knocked on belonged to June Lloyd, whose DNA was in the database because of a DUI arrest.
What did she say to her?
"'We're running a cold case investigation and there are some similarities between your DNA and the offender's DNA. Do you mind telling me, have you got any brothers?' And, she said, 'Yes.' She said, 'I've got a brother, but it wouldn't be my brother. He's a businessman,'" Hickman remembers.
Her brother James was a manager at a print shop. Married, with children, he had no criminal record. But when his sister called and told him about Hickman's visit, he became suicidal, and his family called the police.
Underneath a trap door at his office, police discovered more than 100 women's shoes, all worn, all different sizes, all stiletto heels. DNA testing confirmed James Lloyd was the "shoe rapist."
Hickman had visited three people and solved the crime in eight hours.
Mitch Morrissey believes familial searching should become national policy. "There should be a familial searching policy that is constitutional and legal in the United States," he tells Stahl.