I was a little confused when district attorney candidate Larry Krasner said he wanted to change the culture in that office.

I thought the "culture" was locking up bad guys — but that was before former District Attorney Seth Williams became one of the bad guys.

I know that some prosecutors have played dirty. Every profession — even mine — has a pocket of corner-cutters who will do anything to win.

The DA's Office is not supposed to be in the "winning" business. It is supposed to be in the justice-delivery business. I have written these words before, directed to then-DA Williams, who didn't want to listen.

Whatever reservations I have about Krasner, I think he will listen to this: Marcus Perez, 47, Graterford inmate BH-1591, is doing life without parole because of a Common Pleas Court judge's mistake.

The judge, Theodore McKee, who went on to become chief judge of the U.S. Court of Appeals for the Third Circuit, told Perez he would not die in prison if he took a plea bargain. McKee told Perez he could expect to serve 17½ to 35 years. "I was dead wrong," said McKee, who is deeply embarrassed by his error.

When Perez pleaded guilty to homicide in 1990 and was sentenced to life, McKee did not realize the law had just changed and "life" meant life without parole and not the 17½ to 35 years McKee promised. By the time the error was caught, the case was out of McKee's hands and he was powerless to correct it.

Perez can appeal the mistake, and he has. Many times. Each time an obdurate Williams, more interested in sustaining the botched sentence than in justice, opposed the appeal.

The judge's mistake is one part of this story. There is a second, more troubling, aspect.

Four years after Perez was sentenced, the original transcript was improperly changed after a phone call from then-Assistant District Attorney Jerome Teresinski to the court reporter, who has since died. Neither McKee nor Perez was informed of the change, as is required. The change undercut the basis for Perez's appeal.

Teresinski was not Perez's prosecutor, but he is godfather to one of Williams' daughters. No longer at the DA's Office, he refuses to talk about who requested the transcript change. If you think I am suggesting foul play by the DA, you are right.

The tampering with the record should have gotten Perez a hearing, but it didn't. It's as if no one cares.

Since I started writing about Perez in 2011, I have heard from dozens of inmates with claims of wrongful convictions. Some are con artists, but others weave convincing narratives. For them, there is a conviction review form on the DA's Office website, specifically for wrongful convictions.

Perez was not wrongfully convicted. As a stupid, hot-headed teenager, he pulled a trigger. He admits his guilt and expresses contrition. He's earned his high school diploma in prison and has taken almost every vocational course available to prepare himself for a day that might never come — his release.

It can't come as long as his sentence is life. He has served 28 years and would serve without complaint the maximum of 35 that McKee had mentioned. Perez prays he can get relief and someday be a father to daughter Shannon and a grandfather to granddaughter Khylei.

McKee will testify on Perez's behalf. I've got a file of columns going back to 2011 to share with anyone in the DA's Office who is interested in delivering justice.

Assuming that's what Krasner's culture change is all about.