ERIE — A man admitted Wednesday in federal court that he helped plot a bizarre bank robbery that ended when a bomb strapped around a pizza deliveryman's neck exploded and killed him, the first conviction in the five-year-old case.

Kenneth Barnes, 54, could be sentenced to life in prison, but his attorneys hope he will get a lighter sentence in exchange for his cooperation.

Barnes admitted he was one of the lookouts at the bank and that he offered to build a pipe bomb with a timing device.

The plot unfolded when Brian Wells, 46, walked into a PNC Bank branch on the outskirts of Erie on Aug. 28, 2003, with a pipe bomb locked onto his neck. He presented a teller with a note demanding money and walked away with about $8,700. He died when the bomb exploded as police waited for a bomb squad to arrive.

Last year, federal authorities announced charges against Barnes and the woman they labeled the ringleader, Marjorie Diehl-Armstrong. A federal judge recently ruled Diehl-Armstrong, 59, is mentally unfit to stand trial.