PITTSBURGH — A pizza deliveryman who robbed a bank while wearing a collar bomb that later exploded and killed him had his neck measured for the device, and earlier took part in talks about wearing a fake explosive, according to a document unsealed Wednesday.

The details support authorities’ belief that 46-year-old deliveryman Brian Wells was knowingly involved in the plan to rob the bank.

Wells has been named an unindicted coconspirator in the August 28, 2003, robbery, although U.S. Attorney Mary Beth Buchanan has said his role might have “transitioned from that of the planning stages to being an unwilling participant in the scheme.”

The information was part of an application and affidavit for a search warrant. It also alleges Marjorie Diehl-Armstrong, 58, charged last week in connection with the bank robbery, told a witness in prison that the late William Rothstein, also an unindicted coconspirator in the case, helped make the bomb that killed Wells. Information about the warrant was first reported Wednesday on the Web site of the Erie Times-News, which obtained the documents.

“Diehl-Armstrong also told [the witness] that Rothstein and Wells knew each other and stated ‘they’ even measured Wells’s neck for the device,” the affidavit states. “Diehl-Armstrong further stated Wells had knowledge of the plan, but did not know the extent of his participation.”

Wells told police he had been forced at gunpoint to wear a time bomb around his neck and rob the bank. The device exploded while police waited for the bomb squad to arrive, killing Wells.

Wells’s family insists that he had nothing to do with the plot and did not know the suspects.

The search warrant was for the home of Kenneth Barnes, also charged last week with robbery, conspiracy, and a firearms violation in connection with the heist at PNC Bank in Summit Township. Barnes, 53, who is jailed in Erie County on unrelated drug charges, and Diehl-Armstrong have pleaded not guilty.

Diehl-Armstrong was linked to the Wells case after the body of her boyfriend, James Roden, was found in a freezer in Rothstein’s home near where Wells made his final delivery. Diehl-Armstrong is serving seven to 20 years in a state prison after pleading guilty but mentally ill to killing Roden in 2003. Rothstein died of cancer in 2004.

According to the affidavit, Barnes told investigators he and four others — including Wells, Rothstein, and Diehl-Armstrong — met the day before the heist at Rothstein’s house. There, Barnes “overheard parts of the plan, including that Wells was to wear a fake explosive device into the bank.