The only surviving convicted criminal in the April 19, 1995, bombing of the Alfred P. Murrah Federal Building in Oklahoma City is saying his co-conspirator, Timothy McVeigh, told him he was taking orders from a top FBI official in orchestrating the bombing.

A declaration from Terry Lynn Nichols, filed in U.S. District Court in Salt Lake City, has proven to be one of the most detailed confessions by Nichols to date about his involvement in the bombing as well as the involvement of others. However, one congressman who has investigated the bombings remains skeptical of Nichols' claims.

The declaration was filed as part of Salt Lake City attorney Jesse Trentadue's pending wrongful death suit against the government for the death of his brother in a federal corrections facility in Oklahoma City. Trentadue claims his brother was killed during an interrogation by FBI agents when agents mistook his brother for a suspect in the Oklahoma City bombing investigation.

The most shocking allegation in the 19-page signed declaration is Nichols' assertion that the whole bombing plot was an FBI operation and that McVeigh let slip during a bout of anger that he was taking instruction from former FBI official Larry Potts.

Potts was no stranger to anti-government confrontations, having been the lead FBI agent at Ruby Ridge in 1992, which led to the shooting death of Vicki Weaver, the wife of separatist Randy Weaver. Potts also was reportedly involved in the 51-day siege of the Branch Davidian compound in Waco, Texas in 1993, which resulted in a fire that killed 81 Branch Davidian followers.

Potts retired from the FBI under intense pressure and criticism for the cover-up of an order to allow agents to shoot anyone seen leaving the Weaver cabin at Ruby Ridge.

When contacted, the FBI's main office in Washington, D.C., said it could not provide immediate comment on Nichols' claims Tuesday.

Nichols claims that, in December 1992, McVeigh told him that "while he was serving in the U.S. Army, he had been recruited to carry out undercover missions."

In the next few years, the two men hatched the bombing plot. In October 1994, "McVeigh and I stole explosives from a quarry in Marion, Kansas consisting of 8 1/2 cases or boxes containing 229 (2-inch by 16-inch) sticks of the gel type explosive known as Tovex," Nichols wrote, adding that only a small amount was used in the actual bombing.

It was while traveling the gun-show circuit that Nichols claims the two obtained bombmaking knowledge and the materials used in the bombing. One example is that McVeigh allegedly attended a gun show in Knob Creek, Ky., in 1993.