Nichols, who claims the FBI improperly withheld information on the bombing that could have helped his defense, was back in court Wednesday in a bid to win a new trial.
Nichols, 44, was convicted in 1997 of conspiracy and involuntary manslaughter in the bombing of the Alfred Murrah Federal Building. He is serving a life sentence.
Timothy McVeigh, his former Army buddy, has appealed his death sentence on murder and weapons convictions. Prosecutors claimed Nichols helped McVeigh finance the plan, gather the ingredients and mix the bomb used in the April 19, 1995, blast that killed 168 people and injured hundreds of others.
Nichols entered the U.S. District Court shortly before 9 a.m., wearing a light blue shirt and blue blazer. U.S. District Judge Richard Matsch, who presided at the original trial, is hearing the request for the retrial.
NicholsÂ' lawyers are charging that the FBI withheld documents that could have helped in Nichols' defense.
At issue are dozens of FBI lead sheets given to defense attorneys on Dec. 11, 1997, just 12 days before Nichols was convicted. The sheets are used to record information from informal interviews or from callers during an investigation.
Defense lawyer Michael Tigar has argued that several lead sheets contained helpful information that the defense would have pursued.
One sheet, written shortly after the bombing, reported that Michael Fortier "advised that McVeigh purchased racing fuel at a race track in Kingman (Ariz.) and had rented his own shed there."
Tigar has told Matsch in the past that he never challenged the prosecution's contention that the racing fuel was purchased at a Texas track because prosecutors never acknowledged they had conflicting evidence.
It was a painful return for several victims' families, but they wanted to hear how Terry NicholsÂ' attorneys could argue that he deserves a new trial.
With Nichols' wife and mother watching in the courtroom, Tigar told the judge the FBI data is in conflict with court testimony on several key pieces of evidence, including where the racing fuel was purchased to build the devastating bomb.
Prosecutor Sean Connelly countered, "The FBI documents in question would not have changed the trial's outcome - that Terry Nichols' conspiracy was based on overwhelming evidence."
When the hearing ended, victims' relatives agreed, calling the motion for a new trial frivolous.