ERIE — A co-defendant in the collar-bomb death of a pizza deliveryman who robbed a bank might be feigning mental incompetence merely to further delay going to trial, federal prosecutors said.

As proof that Kenneth Barnes might be malingering, prosecutors said in court documents Thursday that he talked about acting "crazy" with a family member who regularly visited Barnes in jail. The relative, unbeknownst to Barnes, told investigators of the prison discussions, prosecutors said.

Barnes, 54, and Marjorie Diehl-Armstrong, 59, were indicted in July on bank robbery, conspiracy and a firearms violation in the August 2003 robbery of a PNC Bank near Erie. Pizza deliveryman Brian Wells, 46, told police he was forced at gunpoint to wear a time bomb around his neck and rob the bank. As officers waited for the bomb squad to arrive, the device exploded, killing Wells.

Diehl-Armstrong and Barnes have pleaded not guilty.

Last month, Barnes' attorneys filed a motion requesting a competency hearing, saying their client was mentally unfit to stand trial. Prosecutors object to such a hearing.

U.S. District Judge Sean J. McLaughlin scheduled an evidentiary hearing on April 17 to determine whether there is reasonable cause to believe Barnes might be incompetent.