Bombing conspirator Terry Nichols (search) has been meeting with the FBI and has revealed additional details about his involvement in the 1995 attack that destroyed the Oklahoma City federal building, his mother said Sunday.

Nichols, serving life in prison on federal and state convictions for the bombing that killed 168 people, acknowledged that he helped Timothy McVeigh (search) acquire ammonium nitrate fertilizer and racing fuel that were combined to make the explosive, and helped assemble the bomb components, said Nichols' mother, Joyce Wilt (search) of Lapeer, Mich.

"That's the extent of it," Wilt said in a telephone interview with The Associated Press. "From there on, he had no knowledge."

McVeigh was convicted of federal conspiracy and murder charges in the bombing and was executed on June 11, 2001.

Prosecutors have contended that Nichols willingly helped McVeigh plan and carry out the bombing. Wilt said she believes others were involved in the bombing and that the FBI is hiding it.

Wilt contends her son suffers from Asperger's Syndrome, a form of autism that allowed him to be easily manipulated by others. She said McVeigh took advantage of Nichols to get him to help with the bombing preparations and that he threatened to harm Nichols and his family if he didn't comply.

"Terry was just being protective of all of us," Wilt said. "It just breaks my heart, because he was a good kid. He got out in the world and people started taking advantage of him."

She said her son didn't know what McVeigh planned to do with the bomb.

"He didn't ask. People with that type of syndrome don't do that," Wilt said. "When you ask him to do something, he just does it."

Citing unidentified sources, The Oklahoman reported Sunday that Nichols acknowledged to the FBI that he robbed Arkansas gun dealer Roger Moore to help finance the bombing and that he thought McVeigh planned to bomb a monument to get back at the federal government.

Based on Nichols' statement this spring, the FBI recovered a .50-caliber sniper rifle taken in the robbery, the newspaper reported citing unnamed sources.

Prosecutors say Nichols stole an estimated $63,000 in weapons and other items from Moore's home that were then sold to help finance the terror plot. Moore, who underwent months of questioning after the bombing, was never charged and denies any involvement.

Gary Johnson, a spokesman for the FBI office in Oklahoma City, would not confirm any talks between Nichols and the agency. "We may make a statement in a few days regarding the recent media reports, but not at this point," Johnson said Sunday.

The lead defense attorney at Nichols' state trial, Brian Hermanson, said he had not been present for any such conversations and would not confirm if any took place, but said it wouldn't surprise him.

"He's not facing the death penalty. It's pretty logical," Hermanson said.