Convicted bombing conspirator Terry Nichols

DENVER (CNN) -- Convicted Oklahoma City bombing conspirator Terry Nichols said Tuesday he will file a second motion for a new trial after his lawyers finish reviewing 12,000 witness statements turned over by prosecutors after he was found guilty.

In a brief filed with the 10th U.S. Circuit Court of Appeals, Nichols' attorney Michael Tigar said he didn't learn that the government had thousands of witness statements until during the trial.

An FBI agent was forced to admit during the trial that a witness described a gray truck at a Kansas lake, where prosecutors contend the bomb was made, and that the official report changed the color to blue. Nichols owned a blue GMC pickup truck.

Aftermath of the Oklahoma City bombing

Tigar said the defense team is busy reviewing the 12,000 statements to see if there are other discrepancies.

"Another motion for a new trial will be filed when a review of these is completed, but this episode illustrates the double standard at work here," Tigar said.

Nichols' first motion for a new trial is scheduled to be heard February 1. Tigar did not say when the second motion will be filed.

A federal jury convicted Nichols a year ago of involuntary manslaughter and conspiracy. He was sentenced to life in prison and ordered to pay $14.5 million in restitution for his role in the destruction of Oklahoma City federal building. He was acquitted of murder, explosives and property-destruction charges.

The April 19, 1995, bombing of the Alfred P. Murrah Federal Building killed 168 people and injured hundreds more.

Reuters contributed to this report.