Updated

An Erie man admitted Wednesday that he helped plan a bizarre 2003 bank robbery that ended with the death of a pizza deliveryman with a collar-bomb strapped to his neck.

Kenneth Barnes pleaded guilty Wednesday to conspiring to rob a bank and to aiding and abetting. He could be sentenced to life in prison.

The pizza deliveryman, Brian Wells, told police he had been forced at gunpoint to lock the bomb onto his neck and rob the bank. He was killed when the device exploded as police waited for a bomb squad.

Barnes' co-defendant, Marjorie Diehl-Armstrong, is accused of masterminding the plot. A federal judge recently ruled she's not mentally competent to stand trial but said that could change depending on how she responds to medication and treatment.

Thursday was the five-year anniversary of the heist, during which delivery man Wells, 46, told police he was forced at gunpoint to wear a pipe bomb locked onto his neck with a metal collar, and ordered to rob a bank just outside Erie.

Police apprehended Wells and the time bomb exploded before a bomb squad arrived, killing him as he sat with his hands handcuffed behind his back in a parking lot.

Last week, Barnes' attorney Jamie Mead would not say whether his client agreed to testify against Diehl-Armstrong, 59, also of Erie.

The collar-bomb charge carries a sentence of 30 years to life in prison, and Barnes faces up to five more years for the conspiracy count, but a lower sentence was possible depending on whether he agreed to cooperate with prosecutors.

Mead insisted his client was "a very minor player in the entire event."

“The problem was that he was still a player, therefore he was involved in the conspiracy,” Mead said Friday. “That's why he was charged with it and that's why he's got to plead guilty to it.”

The indictment says Diehl-Armstrong asked Barnes how to make a pipe bomb the month before the robbery and told Barnes she wanted to use the money from the heist to pay Barnes to kill her father.

Prosecutors have said Diehl-Armstrong was upset about an inheritance dispute.

The indictment doesn't accuse Barnes of helping to make the bomb or the collar.

The day of the heist, Barnes drove Diehl-Armstrong and others involved to various places and, the day before, discussed the plan with the others, the indictment said.

Diehl-Armstrong's attorney, federal public defender Thomas Patton, declined comment on Barnes' guilty plea.

Diehl-Armstrong is serving seven to 20 years in state prison after pleading guilty but mentally ill to killing her boyfriend, James Roden, 45, in the weeks leading up to the bank robbery.

Prosecutors said she killed Roden because she feared he would tell authorities of the plot.

Another ex-boyfriend of Diehl-Armstrong's, William Rothstein, was identified by his initials in the indictment, but has since died of cancer.

Rothstein helped make the time bomb that killed Wells and phoned in the pizza order used to lure Wells to a secluded spot on a dead-end road, the indictment said.

That's where Wells told authorities he was accosted, though police have never said by whom, and forced to wear the bomb.