Washington ? Ten days before Timothy McVeigh was executed, lawyers for FBI lab employees sent an urgent letter to the attention of Atty. Gen. John Ashcroft alleging a key prosecution witness in the Oklahoma City bombing trial might have given false testimony about forensic evidence.

The allegations involving Steven Burmeister, now the FBI lab’s chief of scientific analysis, were never turned over to McVeigh or the trial court, though they surfaced as the judge was considering whether to delay his execution because the government withheld evidence.

The letter, however, was recently turned over to bombing conspirator Terry Nichols, who faces another trial on Oklahoma state murder charges.

“Material evidence presented by the government in the OKBOMB prosecution through the testimony of Mr. Burmeister appears to be false, misleading and potentially fabricated,” said the June 1, 2001, letter to Ashcroft obtained by The Associated Press. The lawyers represented several FBI lab employees, including one who sued after being fired.

The letter cited Burmeister’s testimony in a civil case as evidence contradicting his earlier McVeigh testimony. The letter specifically challenged Burmeister’s testimony that chemical residues found on evidence came only from McVeigh’s bomb, not other sources such as lab contamination.

It was sent to Ashcroft’s general fax number and by courier with the notation “URGENT MATTER FOR THE IMMEDIATE ATTENTION OF THE ATTORNEY GENERAL.”

Justice officials said Wednesday the letter was routed to Ashcroft’s clerical office in the Maryland suburbs of Washington, where it sat for nearly two months and then was forwarded to the FBI — well after McVeigh was executed.

Neither Ashcroft nor other top officials in the Justice Department who handled the McVeigh case saw the letter, spokeswoman Barbara Comstock said. It was never reviewed to determine whether it should be handed over to McVeigh’s lawyers, officials said.

Justice officials could not explain how a letter marked for urgent attention by Ashcroft on an issue that was dominating the headlines could be misrouted, except to say that the outside lawyers should have done more than send it by fax and courier.