“I think about her a lot,” she told me the last time I saw her. She had dyed her hair pink since my previous visit. “I wonder how it would have been if she were here. You know, right now. The two of us running around, you know what I mean?”

On a chilly May morning, on a street not far from where Holly was murdered, Jennifer Linzer, from the Center on Wrongful Convictions at Northwestern University, and Cynthia Estes, a private investigator, visited the home of a man who was arrested for sexually assaulting a boy shortly before Holly was killed. They began by asking what he remembered about the evening of Holly’s murder, which wasn’t much. They talked about his criminal record, and he pointed out that he liked boys, not girls. Then they asked him if they could get a saliva sample in order to eliminate him as a possible suspect through DNA testing.

“I said, ‘This case is probably coming around again, and we are going to give a list to the cops of people who they should look at and test,’ ” Linzer said. “He said: ‘Great. I’ll do it.’ ”

Rivera’s lawyers would like to obtain a new trial with a different judge. They believe the judge who presided over the previous three trials unfairly favored the prosecution and should not have allowed prosecutors to introduce evidence about Holly’s alleged sexual past, among other supposed judicial errors. But even if Rivera is granted a new trial, with a new judge, there is a realization among his supporters that he could once again be convicted. The crime is simply too heinous, the confession too powerful.

Perhaps the only way to win Rivera’s freedom is to prove that someone other than Rivera killed Holly Staker. Which is where Linzer comes in. The wife of Northwestern’s provost, Linzer began working as a volunteer at the center a decade ago, after she grew restless as a stay-at-home mom. Before the end of the year, she was working full time, organizing files, directing student volunteers and reviewing innocence claims from inmates. She heard about Rivera’s case and eventually began speaking regularly to him on the telephone.

When Rivera lost his third trial, Linzer compiled a spreadsheet of potential suspects and, along with Estes, set about trying to find a killer by asking potential subjects for DNA samples. There are plenty of leads within blocks of the murder. Police reports show that at least two other men told friends that they killed Holly, one of them saying he stabbed her so many times he got tired. There were also at least three convicted sex offenders in the neighborhood, one of whom was convicted of molesting his 11-year-old stepdaughter, and around the corner was a boarding house full of transients. An elderly man a few blocks away supposedly drove around the neighborhood naked and masturbating. When police arrived to interview him, there was a picture of Holly and an envelope with her name on it in his house. A high-school senior had a picture of Holly, too, tucked in his wallet.

“Either this crime touched a lot of people, or there is an inordinate number of perverts in town,” Linzer said.