Long before "Making a Murderer," wrongly convicted prisoner Anthony Porter grabbed national headlines, spending nearly 17 years on death row before his murder conviction was overturned. But now a lot of people think this free man may have been guilty of the crime.

Crime Watch Daily investigates "A Murder in the Park."

Anthony Porter may be the luckiest man on earth. He was convicted of a grisly murder, and his clock on death row was ticking. Porter was just 48 hours away from being executed. Then somebody else confessed.

It's the subject of "A Murder in the Park," Showtime's sensational tale of a single-minded pursuit of justice that goes barreling off the rails.

After 17 years on death row, Porter walks into the arms of the man who freed him: Dr. David Protess.

The good doctor engaged a team of his star Northwestern University journalism students to find the real killer in Porter's case. And when they found the man who confessed to the crimes, Alstory Simon, Porter breathes free, and it seems justice prevails.

But there's a catch.

TV and film producer Shawn Rech combed through reams of court documents and hours of testimony to reveal the untold truth of this explosive story.

And even for the veteran true-crime producer, he was blown away by what he found.