He was a shadowy figure in a sketch, the subject of a nationwide manhunt in the Oklahoma City bombing. Timothy McVeigh says John Doe No. 2 does not exist, but the FBI's failure to disclose evidence has revived questions about whether an accomplice might have gone undetected.

Lawyers for Terry Nichols, convicted as a co-conspirator in the bombing, have asked the U.S. Supreme Court to reconsider his appeal, citing the FBI's recent disclosure that it withheld documents from the defense.

Some of these materials apparently are related to the FBI's huge search for a John Doe No. 2 suspect. Sketches of a dark, heavyset man circulated after the bombing, but federal officials eventually identified him as an Army private who had no role in the attack.

However, some people — including McVeigh's former attorney — still believe there was a John Doe No. 2, and legal experts say the FBI blunder opens a new avenue for Nichols' defense, which had always claimed that there was such a man and that his existence shed doubt on Nichols' role.

"It's a lifeline," said Scott Robinson, a Colorado legal analyst who attended the Nichols and McVeigh trials. "Nichols' lawyers were scrambling to find anything else to work with and the government has really handed them a basis for appeal on a platter."

Nichols is serving a life sentence for conspiracy and involuntary manslaughter.

Larry Mackey, a former prosecutor in both trials, said a jury did not buy defense claims that a mystery man — not Nichols — was involved in the bombing. And he scoffed at those who say an accomplice is lurking out there.

"There's nothing that could have been more important than to find each and every person responsible," he said. "Are there other criminal conspirators? To that question, I give an emphatic no."

But Mackey, now in private practice, also said the bombing is the kind of case that keeps conspiracy theories flying. "There will always be a grassy knoll in Dallas and a John Doe 2 in Oklahoma City," he said.

McVeigh himself has emphatically denied the existence of a John Doe No. 2, contradicting his former attorney, Stephen Jones, who contends McVeigh was among a group of conspirators in the April 19, 1995, bombing that killed 168 people.

"Does anyone honestly believe that if there was a John Doe 2 (there is not), that Stephen Jones would still be alive?" McVeigh wrote in a letter to the Houston Chronicle. "Think about it."

"Jones has been thoroughly discredited, so I'm not going to break a sweat refuting his outlandish claims point-by-point," McVeigh said in the letter, dated May 2 and sent from the federal prison in Terre Haute, Ind. "The truth is on my side."

But Jones maintains John Doe No. 2 is real, and contends he was killed in the bombing. He believes McVeigh is trying to exaggerate his importance in the attack, the deadliest act of terrorism ever on U.S. soil.

"He wants to enlarge his role," Jones said in a telephone interview. "He prefers demonization to oblivion. He's protecting the others."

Jones said several witnesses reported seeing McVeigh with a man other than Nichols at a Kansas motel and other locations in the days before the bombing.

Jones, who wrote a book called "Others Unknown: The Oklahoma City Bombing Case and Conspiracy," also dismissed McVeigh's suggestions that a real John Doe No. 2 would have killed him as the stuff of a "dime-store pulp fiction novel."

McVeigh's May 16 execution was postponed until June 11 after the FBI disclosed last week it had not provided the defense thousands of pages of investigative materials.

Many of those documents were generated in the early hours of the investigation, when agents were chasing leads about the identity of a possible accomplice dubbed "John Doe No. 2."

McVeigh, depicted in another sketch as a stone-faced man with a crew cut, was John Doe No. 1.

The mystery of John Doe No. 2 intensified in the weeks after the bombing when federal officials released sketches of a muscular-looking man with a short neck, square jaw and tattoo seen at the Kansas body shop where McVeigh rented the Ryder truck used to carry the 7,000-pound bomb.

Thousands of tips poured in, with the list of possible suspects expanding into a growing fraternity that included an AWOL solider in California, a drifter in a Missouri motel and an Arizona fugitive. There was even brief speculation that Nichols' 12-year-old son, Josh, was the unidentified man.

In June 1995, authorities identified a 23-year-old soldier as the man in the John Doe No. 2 sketch and cleared him of any involvement in the bombing. He resembled the composite drawing and wore clothes similar to those shown — including a Carolina Panthers cap.

Federal prosecutors later said that the soldier had rented a truck at the body shop the day after McVeigh and that a mechanic apparently was confused, thinking the two men were there together.

But that conclusion does not satisfy Jones.

He said it isn't unusual for it to take years, even decades, to find all the culprits in a crime.

"As soon as they get evidence on the others," he said, "they'll be happy to change their opinion."

But Mackey said while it's natural to think this enormous crime had to be committed by an "organization of equal magnitude," no vast conspiracy exists.

"Have we gotten to the bottom of this? Have we found everybody?" he asked. "Absolutely.'