Mr. Tepfer noted that Mr. Douglas, who was in the neighborhood when the body was found and was interviewed by the police at the time, “preyed on at-risk women, on prostitutes, and he engaged in sex and strangled them to death. It’s just an identical situation.”

But Anita Alvarez, the state’s attorney, said a DNA match was not automatically cause for dismissal of the convictions. “DNA evidence in and of itself is not always the ‘silver bullet’ that it is sometimes perceived to be,” Ms. Alvarez said.

Mr. Douglas, she said, who was shot to death in 2008, was “the type of person that was utilizing prostitutes. He didn’t kill every other prostitute he was with.”

“As a prosecutor, I have a duty to the victims in this case,” she said. “I have a duty to look at everything and weigh it.”

Mr. Swift, now 34 and on parole, said his own confession came out of terror and exhaustion after being questioned for hours by the police, who told him, he said, that if he worked with them and signed the confession he could go home but if not, he would go to prison for the rest of his life.

“I was 17, I’d never been in any type of trouble like that,” he said. “I didn’t know the weight or the magnitude of what a confession could do. It cost me 17 years of my life.”