Brian Wells, 46, told police before the bomb killed him in August 2003 that he was innocent and had been forced at gunpoint to wear the bomb.
"I'm not lying. It's going to go off," Wells said.
But in indictments unsealed Wednesday, Wells is named as a co-conspirator along with Marjorie Diehl-Armstrong and her friend, Kenneth E. Barnes.
"It was the participants' intention to have it seem as though the person wearing the explosive device was a hostage," U.S. Attorney Mary Beth Buchanan said.
It was the first time authorities have said they believe he helped plan the heist.
"Liar!" exclaimed Wells' sister Barbara White. "What if somebody bolted a bomb around your neck, Mary Beth? What would you do?"
Wells' brother John said prosecutors were not doing their jobs and vowed that "the truth will come out."
"Where is the evidence? There is no evidence. You cannot link a man when there is no evidence," John Wells said, his voice trembling with anger. "When he was accosted at gunpoint, taken from his job, that's not a co-conspirator."
"Brian did not put that collar on himself," he said.
"There were opportunities when he could have let people know what was happening and that is why he was both a participant and a victim," Buchanan said at her news conference.
Officials admit they aren't sure how Wells got involved and say there is evidence suggesting he tried to back away from participation at some point, reports CBS News correspondent Cynthia Bowers.
"I think the conventional wisdom will be that he got snookered into this, maybe by being offered a very small amount of money or some compensation, but didn't buy into the fact that there was going to be a real bomb around his neck and he would eventually be killed," CBS News legal analyst Mickey Sherman said on CBS News' The Early Show. "I don't think he knew what he was getting into."
Diehl-Armstrong is already serving time for the murder of her boyfriend, James Roden, whose chopped-up body was found in a freezer during the investigation into Wells' death.
In the indictment, authorities say she killed Roden to keep him from disclosing details of the robbery plot.
"The brutality and utter lack of respect for life displayed by the indicted is rarely seen outside of a movie script," said Mark Potter, special agent in charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives office in Philadelphia.
Both Diehl-Armstrong, who is currently serving a prison sentence for killing her boyfriend, and Barnes are charged with bank robbery, conspiracy and a firearms count.
"I had no part in this," Barnes said as he was led to FBI offices Thursday morning for processing, the Erie Times-News reported. He pleaded not guilty at his arraginment.
Barnes, 53, is jailed in Erie County on unrelated drug charges. Authorities have described him as Diehl-Armstrong's fishing companion.
"Everything is designed to get those two people," Sherman told Early Show co-anchor Julie Chen.
"Marjorie Diehl-Armstrong got a pretty small sentence in her last case on the killing of the boyfriend," Sherman said. "So I think the U.S. Attorney wants to make sure she does not see the light of day outside of prison and they're using everybody they can and unfortunately this Wells is a little bit of collateral damage."
Diehl-Armstrong, 58, wanted the money so she could pay someone to kill her father, authorities said.
"I've been told she's wanted to kill me before," Howard Diehl told the Erie Times-News. "She figured if she killed me ... she'd have this house ... She's got a demented mind. If she wanted a million dollars, she wouldn't ask me for it. She'd try to kill me."
The indictments say Diehl-Armstrong and Barnes contrived a series of notes to make Wells appear to be "merely a hostage," and that he would be able to claim he was an unwilling participant if he was caught. According to the indictments, they locked a live bomb onto Well's neck to ensure he turned over the money.
"If he died, he could not be a witness," authorities said in the indictment.
The bomb that killed Wells was on a timer, but it was unclear if his co-conspirators planned on his death, Buchanan said Wednesday. She described Wells as having a limited role in the plot and said she couldn't comment on what his motive might have been.
"Sadly, the plans of these other individuals were much more sinister ... and he died as a result," Buchanan said. "It may be that his role transitioned from that of the planning stages to being an unwilling participant in the scheme."
On Aug. 28, 2003, Wells set out to deliver an order for two pizzas from Mama Mia's Pizza-Ria to a mysterious address that turned out to be the location of a TV tower. He turned up about an hour later and roughly two miles away at a PNC Bank branch in Summit Township, with a note demanding money and saying he had a bomb.
Wells took $8,702 from a teller, got into his car and was surrounded by police a short time later in a parking lot. State troopers pulled him out of the car and handcuffed him. Hanging from his neck under his T-shirt was a triple-banded metal collar and a device with a locking mechanism that kept it in place. Attached to the collar was a bomb.
"It's going to go off," Wells said. "I'm not lying."
He said someone had started a timer on the bomb and forced him to rob the bank.
While police waited for a bomb squad, the bomb exploded, killing Wells. Police found a gun resembling a cane in the car and a nine-page handwritten letter that included detailed instructions on what Wells was to do with the bank money and how he could unlock the collar by going through a kind of scavenger hunt, looking for clues and landmarks.
The note also included a list of rules and a threat that Wells would be "destroyed" if he failed to complete his mission.
Buchanan said Wednesday that while Wells was in the bank, Diehl-Armstrong and Barnes had watched from across the street, and Diehl-Armstrong was later seen twice along the route described in the notes.
Jim Sadowski, a former co-worker of Wells, said he doesn't believe his friend could have been involved.
"I worked with him and I knew him. I just don't see him doing anything like that. He was a nice person," Sadowski said.
Diehl-Armstrong has been linked to the Wells investigation because her boyfriend's body was found in the freezer of a home near the TV tower where Wells made his final delivery. She pleaded guilty but mentally ill to killing Roden and is serving a sentence of seven to 20 years in state prison.
The man who owned the home, William Rothstein, was questioned in Wells' death but died of cancer in 2004.
Diehl-Armstrong's attorney Lawrence D'Ambrosio has said he believes she had nothing to do with Wells' death but may have known the people behind the robbery.