"Really, all I could think when I saw 'Stacy' on the phone was he was killing her while I was standing there," Morphey told "GMA."
Morphey said he was never certain whose cell phone he was holding.
"I believe it was Drew's phone. I believe Drew, more than likely had Stacey's phone. ... I believe he was setting up pings. Cell phone tower pings" to create a location for himself at the time of Stacy's disappearance, Morphey said.
According to Morphey, within an hour Peterson returned to pick up Morphey and to retrieve the phone. Morphey again tried to tell Peterson he had had enough.
"He said you got a minute? We need to run to the house. I need a hand with something," Morphey claimed Peterson said to him. "I wanted no part of going to his house, so I said no, I need to go home. Well, he said it would just take a second and he drove to his house."
Morphey told "GMA" that when they reached Peterson's house, the former Illinois cop went into his bedroom and emerged a few minutes later muscling a large blue barrel out of the room. He needed Morphey's help in getting the barrel down the stairs without tipping it.
He said the two men carried the barrel outside and put it in the back of Peterson's truck.
"I got in the car as soon as we left it there. ... I didn't even turn my head. I just looked straight ahead thinking ... my God, what's going on?" Morphey told "GMA."
When Peterson dropped Morphey off at his home, he said ominously, "This never happened," Morphey claimed. "I said I won't say a word."
When asked if Morphey knew where Peterson went with the barrel, he said, "I wish I did. Sometimes I wish I had rented that locker just because we'd know where she was."
But he also suspects Peterson's motives.
"On the other hand, I partially think that locker was to be put in my name so he could set me up," Morphey said.
Morphey was tormented by what he believed had taken place, possibly with his help.
"I knew I had had a part and granted, I didn't kill her. I helped him carry it and it just didn't sit good with me at all. I was beside myself," he told "GMA."
Morphey tried to commit suicide the next day by taking an overdose of pills. His wife drove him to the hospital, and a brother helped him go to the police.
Peterson has not been charged with any crime, but a grand jury has been convened to decide whether to indict Peterson for Stacey's disappearance. And Savio's death has been reclassified as a homicide.
Peterson maintains that his wife ran away with another man, and Morphey is concerned about what kind of case can be made, since the police don't have a body. So far, he has not been called to testify before the grand jury.
"I think they're doing everything in a timely fashion, and when they feel the time is right for me to go, I hope to be able to be there," Morphey said.
Peterson's lawyer Joel Brodsky has scoffed at Morphey's tale and cites his history of drug addiction and alcohol abuse.
"If they found him credible, [Morphey] would have been one of the first witnesses they would have brought in and they would have based the entire investigation and the entire case on his testimony," Brodsky said at a news conference called to rebut Morphey's first public allegations against his stepbrother.
Brodsky predicted that Morphey won't ever see the inside of a courtroom because prosecutors won't risk calling him as a witness.