updated 4/29/2004 10:52:20 PM ET 2004-04-30T02:52:20

An FBI scientist testified Thursday at the murder trial of Oklahoma City bombing conspirator Terry Nichols that he discovered explosive residue embedded in a single piece of a truck used to deliver the bomb to the federal building.

Steve Burmeister, head of the scientific analysis unit at the FBI laboratory, and other investigators have said ammonium nitrate fertilizer was also discovered during a search of Nichols’ Kansas home three days after the April 19, 1995, bombing of the Alfred P. Murrah Federal Building. Nichols was at his home the day the bomb was detonated.

Prosecutors say Burmeister’s discovery is key to proving Nichols helped executed bomber Timothy McVeigh gather components and build the giant fertilizer bomb used in the attack, which killed 168 people. Ammonium nitrate is key to making such a bomb.

A photograph of the wooden debris with the microscopic crystals was shown to Nichols’ jury over television monitors in the courtroom. The plywood came from the cargo container of the Ryder truck that delivered the bomb and is the only direct evidence of the explosive used.

Here, then gone
Burmeister said he concluded a month after the bombing that the explosion was caused by a fertilizer bomb. But the microscopic crystals that helped him reach that conclusion were gone when the plywood was examined again in November 1996.

“I went to the area where I knew it to be present, and it wasn’t there,” he said. “They dispersed. They went away. They dissipated.”

Defense attorneys believe the truck fragment may have been contaminated in FBI lab tests and that it is impossible to determine who may have handled it because of the way the evidence was stored.

On cross examination, Burmeister speculated that the crystals may have fallen or been knocked off the wood, or come in contact with moisture and been absorbed into the atmosphere.

Defense attorney Barbara Bergman questioned Burmeister at length about how the crystalline evidence survived a violent thunderstorm that drenched Oklahoma City a few hours after the bombing.

‘Other explanations’ for absence
Burmeister said the area containing the crystals was facing the ground and was protected from the elements.

Bergman also questioned Burmeister about whether the crystals could have become embedded by some means other than an explosion. “There could be other explanations. I don’t know what that could be,” he said.

Prosecution evidence is expected to conclude Friday. The defense case is scheduled to begin May 6.

Nichols, 49, is already serving a life prison sentence after a federal jury convicted him of conspiracy and the involuntary manslaughter of eight federal agents in the bombing.

In Oklahoma, he is charged with 161 counts of first-degree murder for the deaths of the other 160 victims and one victim’s fetus. Prosecutors are seeking the death penalty.

McVeigh was convicted on federal murder charges and executed in June 2001.

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