ERIE, Pa. — A pizza deliveryman who robbed a bank and was then blown up by a bomb locked around his neck helped plan the robbery and then got caught up in something “much more sinister,” a federal prosecutor said yesterday.

The deliveryman, Brian Wells, 46, had told police before the bomb exploded in August 2003 that he was an innocent victim and had been forced by gunmen to rob the bank.

However, in the indictments unsealed yesterday, Wells is named as a co-conspirator. Two other people, Marjorie Diehl-Armstrong and her friend Kenneth Barnes, are charged with bank robbery, conspiracy, and a firearms count. Authorities said the plot was concocted so Diehl-Armstrong, 58, could pay someone to kill her father.

Diehl-Armstrong and Barnes are accused of contriving a series of notes to make Wells appear to be “merely a hostage,” according to the indictments.

Their plan was to get the money from Wells in a way that if he was caught, he could claim he was an unwilling participant, authorities said in court papers. According to the indictments, they locked a live bomb onto Well’s neck to ensure he followed their instructions and turned over the money.

“If he died, he could not be a witness,” authorities said in the indictment.

U.S. Attorney Mary Beth Buchanan described Wells as having a limited role in the plot and couldn’t comment on what his motive might have been for being involved. The bomb that killed Wells was on a timer but it was unclear if his co-conspirators planned on his death, she said.

“Sadly, the plans of these other individuals were much more sinister … and he died as a result,” Ms. Buchanan said. “It may be that his role transitioned from that of the planning stages to being an unwilling participant in the scheme.”

Diehl-Armstrong is currently serving a state prison sentence for killing her boyfriend, James Roden. In the indictment, authorities say she killed Roden to keep him from disclosing details of the robbery plot.

Barnes, 53, is jailed in Erie County on unrelated drug charges. Authorities have described him as Diehl-Armstrong’s fishing companion.

Diehl-Armstrong was notified Tuesday that she may face charges of bank robbery, conspiracy, and a firearms count, lawyer Lawrence D’Ambrosio said. He says she is innocent.

Wells set out to deliver an order for two pizzas to a mysterious address that turned out to be the location of a TV tower on August 28, 2003. 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 Geo Metro 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.

Ms. Buchanan said yesterday 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 coworker 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,” Mr. 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 her boyfriend 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’s death but has since died of cancer.

Mr. D’Ambrosio, Diehl-Armstrong’s attorney, has said he believes she had nothing to do with Wells’s death but may have known the people behind the robbery.