HOUSTON - A courthouse seems the last place Michael Anthony Green would choose to spend his time after his release over the summer from a Texas prison where he spent 27 for a rape he didn't commit.

But each weekday, Green walks past metal detectors and police officers in the lobby of the Harris County Criminal Justice Center and makes his way to the 20th floor. There, he sits in a small office and pores through letters written by inmates discussing possible problems with their cases.

Since his release in July, after new DNA tests showed he was innocent, Green has worked for his attorney as a volunteer, reading letters from inmates, looking for others who might be wrongfully imprisoned.

"We might find a case where there's another me that I can help," Green, 45, said.

According to the Innocence Project, a New York legal center that uses DNA to challenge convictions, 261 inmates in the United States have been exonerated after conviction through DNA, most of them since 2000. Texas leads the nation, with 40 cases. After Green's release, his attorney, Bob Wicoff, approached him about helping him review cases.

Wicoff said he became impressed with Green's knowledge of the law during their prison visits. "It was pretty apparent he knew a lot more law than any other inmate I've met," Wicoff said.

Each day, Green reads inmate letters and fills out a two-page form that summarizes the claims and whether they have merit. He looks for cases where DNA could play a factor. A typical letter is one written by an inmate convicted of rape. The inmate claims the victim filed charges because he broke his promise to give her illegal drugs. The inmate also claims he had a bad attorney.

"He doesn't deny having sex, but that it was consensual," Green said, a stack of other letters next to him. "There is nothing that can be challenged, other than the ineffective assistance of counsel. But that is his word against the attorney's."

Green said most of the letters he reads are about burglary, robbery, and murder cases in which inmates claim they are innocent but in which nothing can be done because either there is no DNA to test or such testing wouldn't make a difference.

Wicoff said that although their focus was on DNA cases, they were also on the lookout for other potential legal problems.

Once motivated by anger, Green said he was now driven by a need to help others who might have been wrongfully convicted and by, of all things, a love of the law.

That passion began, oddly enough, after Green was convicted in 1983 for raping a woman who had been abducted by four men from a pay phone in north Houston and taken to a remote spot. Green was detained by officers that night as he walked in the area.

The victim misidentified Green as one of her abductors. He was convicted of aggravated sexual assault and sentenced to 75 years. The only person convicted in the case, he entered prison four months after turning 18.

"My first three years in prison, I didn't do nothing but act a fool. I was mad about being in prison," Green said.

After getting into trouble in October 1985, he was sent to administrative segregation, where he stayed locked up in a tiny cell 22 hours a day. There, Green decided to take the advice of a fellow prisoner to "go to the law library and find a way to beat your case."

While segregated, Green had law books sent to him. He read them cover to cover but stopped after becoming frustrated about the lack of uniformity in court decisions.

"My New Year's resolution for 1986 was get into the law, and I'm not going to stop this time. From Jan. 3 of 1986, all the way until I got out of prison and working up in here, that's what I did," Green said.

After years of appeals by Green, including some he wrote himself, the Harris County District Attorney's Office reviewed his case and found that DNA evidence on the victim's clothing could not have come from him.

Green said that in the more than 200 letters he has read from inmates so far, he hasn't found one he could help, but that he remained committed to his work.

"This is important, getting somebody out that don't belong in prison," Green said.

Green's need to right judicial wrongs is common among inmates who have been exonerated, said Kimberly Cook, a sociology professor at the University of North Carolina Wilmington who has studied the experiences of those exonerated who were on death row. Their need to bring about social change because of their experiences seems to make their psychological adjustment to life outside prison healthier, she said.

"So if they can use their personal experience to . . . prevent it from happening to other people, then there is some comfort in that," Cook said.

Green's work is voluntary but he said he wasn't worried about money. He is eligible for compensation from the state for being wrongfully imprisoned. But that's a topic he declines to discuss for fear of putting his family in danger.

"I take life one day at a time," he said. "Whatever is happening today, that's what's happening. After today, I move right along."