A Knock On The Door

Detectives Revisit 1982 Murder Mystery

(CBS)  Back in Pelham, Mark began to prepare for his trial, confident a jury would find him innocent.

"And when they see the evidence as it's presented, we think that they'll come to the same conclusion that we know the reality is - that I’m innocent," Mark said.

Sherman was on the offensive, and the defense attorney thought his best evidence is getting his client on the stand to tell the story. "And, a lack of such a story on the part of the state," he says.

But while Sherman was making his plans for Mark's defense, he was unaware that Melinda was making plans of her own.

With few choices, Melinda made a stunning move and turned to prosecutor Paul Morrison, looking for a deal. In exchange for a lighter sentence, she said she'd finally tell the truth of what happened that night her husband was brutally murdered.

Melinda admitted for the first time she took part in the murder of her husband and said she did it with Mark's help. It sounded like big break for the prosecution - but it could be a bigger break for the defense.

"I think it's gonna be great fodder for the defense," argues Hoffman. "You know, she told a lie in '82. She told half truths in 2001. She was convicted in 2005. And now, facing life in prison, she's gonna come clean and tell the truth. Well, do you believe her?"

Sherman admitted he was concerned about Melinda's testimony. "I could put on a big act and say it's no big deal because she's lied before. But of course I'm concerned."

The usually confident Sherman knew this could be trouble. "I mean, this is someone who is obviously going to implicate him. Her credibility, her believability is going to make a great difference in whether or not Mark Mangelsdorf is going to be convicted or acquitted," he explains.