Part II: The Whole Truth?

Mary Howell fears that Kevin Cooper, who's been on California's death row, could die for a crime he didn't commit.

"I still can't believe that one person could do all that to my family," says Mary. "My family was strong ... I want to know why my family was killed. Who did it? And I don't want to die without knowing it."

Finding that truth, however, may be easier today than it was when Cooper went on trial. There are now DNA tests that were not available back in 1985 - tests that can conclusively prove guilt or innocence.

As a result, Cooper is battling with the state of California for those test results. And Mary has joined his fight: "I'll never be satisfied till they give that DNA test, and let's prove it one way or the other."

Paul Ingels, who is on Cooper's defense team, along with several lawyers, is also pushing for DNA tests of critical evidence.

First, there's the drop of blood that state experts said was Cooper's. But Ingels, who questions those findings, says DNA tests will say for sure.

He also wants a DNA test of a cigarette butt found in the Ryens' station wagon. Prosecutors had told the jury that it belonged to Cooper.

"It's tobacco that's typically issued to inmates," says Ingels. "That points to Kevin Cooper again. But the saliva on there ... the saliva will have a DNA profile."

And, there is a beige T-shirt found near the Ryen home shortly after the murders. The front of the garment has blood spots on it, and the blood closely matches that of Doug Ryen, according to Ingels. DNA tests could identify if it was. Plus, with the perspiration in the armpit and the neckline, DNA might be able to pinpoint one of the assailants.

Then, finally, there's dirty blond hair taken from 10-year-old Jessica's hand after she struggled for her life.

Ingels wants that hair tested for DNA since it doesn't appear dark enough to be Jessica's - and it doesn't belong to Kevin Cooper.

But former prosecutor Dennis Kottmeier believes that DNA tests would be a waste of time: "Why should we go through a repetitive process of reexamining every piece of evidence in a trial that is already over?"

"Obviously if there is evidence that is going to make a difference, yes," he adds. "But let's assume that you get a test result on DNA, what are you going to find? That maybe there is some other individual...the blond haired guy. Does that mean that Kevin Cooper is not guilty? Not at all."

But Ingels disagrees: "The entire theory of the prosecution's case is that Kevin Cooper acted alone. For them to now say, 'Oh, well, now he's in cahoots with a gang or something...or some satanic group,' doesn't make sense. Certainly everybody would have to revisit this case and go out and identify these other guilty parties."

That fear - that the killers could still be out there somewhere - is why Mary is pushing for DNA tests. "If somebody out there thinks maybe Josh could identify him, if they went after Josh, they'll go after me too," she says.

But it's not that simple. Ingels believes that since Cooper has been on death row for years, people won't want to admit they made a mistake.

Why this man? Because Furrow's old girlfriend, Diana Roper, believes - as she has since 1983 - that Furrow killed the Ryens. "He's an evil person. You can look in his eyes and see it," she says, claiming that she found bloody coveralls in a closet that she cleaned out a few days after the Ryen family was murdered.

Furrow is a killer. He strangled Mary Sue Kitts, 17, in 1974 and dumped her body in a canal. Furrow copped a plea and met Roper, who was visiting another inmate, while serving a five year sentence.

But there is more. Roper says that Furrow was wearing a t-shirt that was similar to the one that police found near the crime scene. She told authorities about her suspicions and gave deputies the bloody coveralls she found. However, three months later, a Deputy sheriff threw them away before they could be sent to a lab for testing.

48 Hours hired Ingels, who is now leading a law-abiding life.

"I'm willing to talk to anybody," said Furrow, denying his involvement in the Ryen family murder. "There was no coveralls. I wasn't living there."

Furrow, however, admitted that back in 1984 he was questioned by authorities about the Ryen murders but they concluded there was only one killer - Kevin Cooper.

"We deal in concrete facts, not the what ifs. The big question is was there sufficient evidence to illustrate the guilt of Kevin Cooper, and the answer to that is yes," says Kottmeier, who is certain that Furrow didn't kill the Ryens.

Will Cooper be executed? Or will the state allow DNA tests that could set him free?