The evidence included a surveillance videotape of a bank robbery by some of the supremacists that occurred in Ohio five months before the bombing. The FBI lab compared the tape to pictures of McVeigh, but concluded a match was "inconclusive," internal memos show.
The 1999 destruction order, obtained by The Associated Press, was unusual because at the time McVeigh and one of the bank robbers had legal appeals pending.
And the government knew, but had turned aside, an offer from one of the bank robbers, Peter Kevin Langan, to provide information about possible other conspirators in the McVeigh case. Langan and his lawyer claim he still possesses Oklahoma City information the government hasn't heard.
FBI officials said Wednesday they were still trying to determine whether the videotape and other evidence was actually destroyed, but remain confident all those responsible for the 1995 bombing of the Alfred P. Murrah federal building have been punished.
"Every lead, regardless of its credibility, was thoroughly investigated to its conclusions," FBI spokesman Mike Kortan said. "While conspiracy stories continue to circulate, no evidence that other individuals were involved in the bombing was corroborated by the investigation."
Dan Defenbaugh, the retired FBI agent who led the Oklahoma City investigation, said while he was knew about the original effort to link McVeigh to the robbery, he was troubled by the evidence destruction order and unaware of it.
"Normally, all evidence is held by the FBI until the completion of all appeals," Defenbaugh said.
The videotape and connections to bank robbers were among thousands of pages of documents gathered by AP that show FBI investigators in the Oklahoma City case gathered evidence linking McVeigh to white supremacists who the government had been told before the bombing were threatening to attack government buildings.
Some of those supremacists, including the robbers, frequented an Elohim City compound in eastern Oklahoma where a federal informant warned federal law enforcement weeks before McVeigh's bombing that members were agitating to attack the government.
The FBI connected McVeigh to Elohim City through hotel receipts, a speeding ticket, prisoner interviews, informant reports and phone records and strongly suspected in the beginning that members there were familiar with his plan, the memos show.
"It is suspected that members of Elohim City are involved either directly or indirectly through conspiracy," federal agents wrote just days after McVeigh detonated a truck bomb on April 19, 1995, outside the Murrah building and killed more than 160 people.
McVeigh was put to death on June 10, 2001, in the first federal execution in 39 years. He had been scheduled to die about a month earlier, but won a postponement when it emerged that the Justice Department had failed to turn over thousands of documents to his defense team.
McVeigh tried but failed to get an additional stay of his execution; his lawyers argued that some of the 4,500 withheld documents pointed to possible other conspirators.
Several documents obtained recently by AP were not provided to the bomber's defense before he was convicted, and his original lawyer said he believes the omissions kept jurors from considering other possible accomplices in the case.
"They short-circuited the search for the truth," attorney Stephen Jones said. "I don't doubt Tim's role in the conspiracy. But I think he clearly aggrandized his role, enlarged it, to cover for others who were involved."
The documents also include a teletype from FBI headquarters in August 1996 that reported McVeigh called Elohim City two weeks before his bombing, a call to a home where members of the violent Aryan Nation bank robbery gang were present.
McVeigh made the call on April 5, 1995, moments after calling the Ryder truck company where he rented the truck that carried his deadly fertilizer bomb.
The FBI teletype revealed that the gang members were familiar with explosives and had made a videotape three months before McVeigh struck vowing a war against the federal government and promising a "courthouse massacre." The Murrah building was across the street from the federal courthouse in Oklahoma City.
The teletype also noted that two of the robbers left Elohim City on April 16 for a location in Kansas a few hours from where McVeigh was doing the final assembly of his bomb.
Defenbaugh, who supervised the Oklahoma City investigation, told AP he never saw the memo. He said while he didn't consider the teletype a "smoking gun" that would have changed the outcome of the probe, his investigative team "shouldn't have been cut out. We should have been kept in on all the items of the robbery investigation until it was resolved as connected or not connected to Oklahoma City."
Defenbaugh said he also was surprised to learn, from AP interviews and documents, that prosecutors in 1996 made and then withdrew a plea bargain offer to Langan, one of the imprisoned bank robbers.
"The Justice Department came to us through the assistant U.S. attorney and said, 'We believe your client knows about Oklahoma City and we want to talk to him. We want to work out a deal,"' Langan's lawyer Kevin Durkin told AP.
Langan made several demands the government wasn't willing to meet, and prosecutors dropped the request, Durkin said.
Durkin said his client had planned to tell prosecutors that he could disprove the April 19 alibis for two of the bank robbers mentioned in the FBI teletype.
Langan recently asked a court to stop the government from destroying evidence he claims may be relevant to the Oklahoma City case.
"The government also hid evidence from the defense counsel of Timothy McVeigh that it had agreed to turn over," Langan wrote in a recent court filing. "These documents show a link between the Oklahoma City bombing case and government witness(e)s in" the bank robbery case.
FBI officials acknowledged some of the documents were not provided to McVeigh's defense team before his trial. For instance, they said FBI teletypes were not covered by the agreement governing documents for McVeigh's defense.
They also acknowledged that agents suspected at one point that the bomber was linked to Elohim City and the Aryan Nation bank robbers.
But they said that after more than 1 million investigative hours that generated more than 1 billion documents and checked 43,000 tips, FBI agents found no concrete evidence of McVeigh conspirators beyond Terry Nichols, who is in federal prison.
"Even though we had our conspiracy theories, we still had to deal with facts and the fact is we couldn't find anyone else who was involved," Defenbaugh said.
The documents show the FBI suspected McVeigh participated in a December 1994 Ohio bank robbery with the Aryan Nation robbers.
But on March 17, 1999 - while Langan and McVeigh appeals were still pending - the FBI wrote that prosecutors had "advised that they saw no reason to maintain custody of the evidence" in the case. "In view of the above, the evidence will be destroyed," the FBI wrote.
FBI officials had several reasons to suspect a connection:
-McVeigh's sister told them her brother gave her money from a bank robbery and asked her to launder it in December 1994.
-The leader of the robbery gang, Mark Thomas, initially told agents after his arrest that he suspected some of his members were involved in McVeigh's plot. He later recanted.
-A girlfriend of one of the bank robbers told the FBI her boyfriend had told her beforehand of a plan to bomb a federal building, and that he left days before the bombing for a trip to Elohim City. "We are going to get them. We are going to hit one of their buildings during the middle of the day. It is going to be a federal building," the FBI quoted the bank robber as telling the girlfriend.
FBI agents stopped pursuing possible connections between McVeigh and the robbers when the suspects all denied assisting the Oklahoma bomber. Most weren't given lie detector tests, officials said.
The robbers, however, weren't the only evidence that led the FBI to suspect a link between McVeigh and Elohim City.
Agents collected a receipt showing McVeigh stayed at a hotel near the compound on Sept. 13, 1994. The hotel was about 20 miles away in Vian, Okla., one of the closest cities with a hotel near the compound. The FBI also obtained a speeding ticket McVeigh received just 12 miles from the compound.
They also interviewed a witness who had aided government prosecutors in other white supremacist cases.
John Shults told agents in 1997 he was "sure beyond a shadow of a doubt" he saw McVeigh at Elohim City in 1994 at a meeting about a mysterious delivery and the use of a Ryder truck. Shults "felt strongly the delivery may have been a reference to the bombing," according to one federal agent's interview report.
Within a few days of the bombing, FBI officials received intelligence suggesting members of Elohim City had information relevant to the investigation.
A federal informant talked with one compound member who "discussed alibis for April 19, 1995, and the components of" McVeigh's bomb, investigative memos show. The same member had claimed, before McVeigh's bombing, that he had detonated a 500-pound fertilizer bomb, similar to the one McVeigh later used.
That compound member also discussed the name of a munitions dealer that McVeigh's phone records showed the bomber called more than two dozen times in the weeks before the attack. McVeigh had the dealer's phone number in his wallet when he was captured.