FBI Re-Creates Events Leading to Bomb Blast : Probe: Camera sequences help sketch Oklahoma City timeline. They indicate device was lit before truck stopped.

Government investigators have put together a reconstruction of the moments before the Oklahoma City bombing, which indicates that the fuse attached to the bomb was lit inside the rental truck even before the Ryder vehicle came to a stop in front of the federal building.

According to sources close to the case, the re-creation was done with the help of at least two video cameras located near the Alfred P. Murrah Federal Building that captured some of the critical events in the minutes before the April 19 bombing. A total of 169 people were killed and 600 others were injured in the blast.

The investigators, in compiling second-by-second time sequences and measuring distances in front of the building, also concluded that the getaway car may have been less than a block from where the Ryder truck was parked, the sources said.

Earlier, it was believed that Timothy J. McVeigh, charged by the grand jury with parking the truck outside the building and causing it to explode, left his yellow Mercury Marquis far from the scene of the bombing to assure his safety.

By reconstructing the events leading up to the worst domestic terrorism incident in the United States, the FBI’s timeline could prove significant in establishing how the bomb was detonated. But it also could run the risk of tying the government to a precise chain of events that could be attacked at trial by defense attorneys.

Time-sequence reconstruction is often created in major cases, officials said, because it is a helpful investigative tool. It also can become potentially persuasive evidence that can be used by prosecutors in a courtroom.

“Timelines are always important,” said William Baker, former assistant FBI director in charge of the criminal investigative division. “If effective, especially one in minutes and seconds, it obviously will have a significant impact on any juror.”

But Baker, who also served as a high-ranking CIA official and now is president and chief executive officer of the Motion Picture Export Assn. of America in Southern California, warned that defense attorneys often seize on specific details in a timeline to question its overall accuracy.

“They are susceptible to one element being attacked and casting larger doubts,” he said of timelines. “The pitfall is, if you become too assertive on the timeline, you fall into the [O.J.] Simpson problem,” he added, referring to defense lawyers’ attacks on the sequence of events used by prosecutors in the trial to show what happened on the night of the double murders in Brentwood.

It remained unclear this week exactly how much was learned in the FBI’s reconstruction. For instance, it could not be determined whether the reconstructed sequence provides any new details about another possible bombing suspect, known simply as John Doe No. 2.

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Nor was it clear whether the person picked up by the cameras was alone or is even recognizable as McVeigh, or whether the getaway vehicle was parked near the building or was driven there by someone to allow the person or persons in the truck to make a hasty retreat.

“This process is not an exact science,” said one source. “But it is getting us closer to understanding what happened.”

Hoping to settle some of the unanswered questions, investigators sent the film out for electronic enhancement and further analysis.

The re-creation was done by using another Ryder truck to match video footage and still photographs from surveillance cameras mounted in the downtown area near the Murrah building. Inside the truck, they placed barrels similar to those reportedly used to hold the ammonium nitrate for the bomb.

The investigators worked backward from 9:02 a.m., when the bomb went off. They calibrated the clocks to the times shown on at least two surveillance cameras to come as close to the actual times as possible.

For instance, one source said: “We have the Ryder in a frame on the video and we clearly know when the building exploded. But other elements, like the burning of the cord, are estimates.”

According to sources close to the investigation, the FBI has put together this scenario:

* A total of three minutes and five seconds elapsed between the time the Ryder truck was last seen on a surveillance monitor and the bomb exploded.

* The truck traveled about 500 feet in this period. It was estimated that it would take 2 minutes and 14 seconds to go from where it is seen on the video to where it was parked in front of the Murrah building.

* That leaves about one minute between the time the truck was parked in front of the building and the time the bomb exploded.

* The FBI next calculated how long it would take for the fuse to burn and ignite. FBI experts concluded that the fuse was quite long and ran from inside the cab of the truck, where the driver sits, through a hole in the backboard, and then into the truck shell where the barrels were reportedly loaded with ammonium nitrate fertilizer.

* The FBI believes that the fuse was most likely about 10 feet long. That means it would take about 2 minutes and 12 seconds between the time the fuse was lit and the time the bomb ignited. Using that calculation, the fuse had to have been lit before the truck came to a stop in front of the building. In fact, it would mean that the fuse had to have been lit almost a full minute before the truck was parked in front of the Murrah entrance.

“We don’t know for sure on that,” one source said. “But we’re operating on that theory.”

* The FBI believes that the Mercury was parked 80 feet from the Ryder truck, although how they came to that conclusion is unclear. However, in the photos, the bureau labeled the Mercury as the “getaway vehicle” and, in contrast, the Ryder truck as the “suspect vehicle.”

* Investigators believe that it would take someone about 10 or 12 seconds to walk the 80 feet from the truck to the car. Sources emphasized that witnesses have not reported seeing someone run from vehicle to vehicle.

* Finally, the FBI estimated that the Mercury left the scene traveling about 25 m.p.h.--a likely speed because no one saw it leave in a hurry. Using that calculation, the getaway vehicle would have traveled about 4,400 feet, or a little more than 0.8 of a mile, before the bomb exploded.

Serrano reported from Oklahoma City and Ostrow from Washington.

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Three Minutes to Tragedy

Here are the events leading up to the Oklahoma City bombing, based on surveillance cameras around the site, according to the FBI:

3 minutes before: Truck last seen by surveillance cameras 3 minutes and 5 seconds before blast

2 minutes before: FBI believed fuse was lit 2 minutes and 12 seconds before blast.

1 minute before: Truck parked in front of Murrah building about 1 minute before blast.

Blast: Blast at 9:02 a.m., April 19, 1995

FBI believes 10-foot fuse ran from cab to drums of explosives in back of truck.

Sources: FBI, Times Washington Bureau