McAlester, Okla. ? A federal death row inmate who may testify in the state murder trial of Oklahoma City bombing conspirator Terry Nichols says it wasn’t the defendant who helped Timothy McVeigh make the bomb.

Prosecutors contend Nichols and McVeigh made the bomb at a lake in north-central Kansas the day before the April 19, 1995, attack, but David Paul Hammer claims McVeigh told him that other co-conspirators helped him assemble the device the night before in an Oklahoma City warehouse.

“Nichols backed out. He didn’t show up,” Hammer said in an interview with The Associated Press.

Hammer, who served on death row with McVeigh, could bolster the argument of defense attorneys that Nichols was set up by unknown co-conspirators to take the blame for the bombing of the Alfred P. Murrah Federal Building that killed 168 people.

But prosecutors, who are seeking the death penalty against Nichols, 49, will vigorously attack Hammer’s credibility if he takes the stand.

Prosecutors have described Hammer as “one of the least credible sources ever to serve time” in an Oklahoma prison. Assistant Dist. Atty. Lou Keel said Hammer once threatened to kill him and a judge and blow up the Oklahoma County Courthouse.

Testimony is scheduled to resume today in Nichols’ case, which began March 22.

Hammer, 45, who is scheduled to be executed June 8 for killing his cellmate in 1996, claims McVeigh revealed secrets about the bombing plot during almost two years of conversations at the U.S. Penitentiary in Terre Haute, Ind. McVeigh was executed in 2001.

Hammer said McVeigh claimed he planned the attack and gathered components for the ammonium-nitrate-and-fuel-oil bomb with help from a bank robbery gang made up of members of the Aryan Republican Army, a white supremacist group. Defense attorneys may question a member of the gang at Nichols’ trial.

Although Nichols participated in the plot, McVeigh said others were responsible for the theft of explosives from a Kansas rock quarry and the robbery of an Arkansas gun dealer, Hammer said. Prosecutors attribute those activities to Nichols.

McVeigh “said that Nichols did help him gather the stuff and helped him store it,” Hammer said.