168 dead. How many bombers?

Tim Cornwell on the battle to construct alternative 'scenarios' of the Oklahoma City explosion

What Kyle Hunt remembers most from that April morning in Oklahoma City in 1995 was the yellow cloud billowing across the sunlight. When the blast shook his building, right next to the Alfred Murrah office block but sheltered from the main force of the bomb, he ran down six flights of stairs and got outside.

"There was a yellow cast over the sky, that was probably the thing that struck me," said Mr Hunt, a vice-president of the Bank of Oklahoma. "That morning had been a beautiful dark blue morning, after a front moved through and kind of cleaned it up. Five minutes later it was totally changed."

Two years on, he clings to his belief that he had seen Timothy McVeigh half an hour earlier. He told the FBI that the accused bomber, for whose trial jury selection began last week, was driving a yellow Mercury Marquis, slowly following the hired truck alleged to have carried the bomb, in the company of at least three other men. He vividly remembered the man with close-cropped hair who shot him a cold stare when he pulled alongside.

In the early days of the bombing investigation, at least a dozen people emerged who claimed to have seen Timothy McVeigh in Oklahoma City on the morning of 19 April 1995, when a bomb destroyed the city's main federal building, killing 168 people, including 19 children. But none of the dozen, apparently, will be called by the prosecution.

"There's been a lot of circus atmosphere," Mr Hunt said last week. "They are not calling any of the eyewitnesses,and I can understand why they are not." But he was "most definitely" sticking to his story that Mr McVeigh was with someone else. "I'm darn certain of the time that I saw him, and whom I saw."

Two starkly different versions of reality are being sold in the Oklahoma City trial, which has been shifted to Denver. When the jurors are finally seated, the prosecution will come to them with a tale of a kitchen-table bomb plot hatched by three disgruntled 28-year-old ex-army men, fired by hatred of the government and burning with rage over the botched federal siege of heavily armed cultists at Waco, Texas.

The government's star witness against Mr McVeigh - and, in a subsequent trial, his co-defendant Terry Nichols - will be Michael Fortier, the best man at his wedding. Mr Fortier turned state's evidence in exchange for a reduced sentence and immunity for his wife, Lori. He is expected to tell how they cased the target together after Mr McVeigh wrote to him asking for help in 1994.

The defence, for its part, is expected to portray Mr McVeigh as the fall guy, a pawn in a plot embracing right-wing supremacists, Middle Eastern terrorists and even the IRA. His 14-strong legal team, at a cost of $10m (over pounds 6m) to the US government, has been chasing leads in Ireland and Israel. Just how far the defence will dare to take this tack with jurors remains to be seen, but against a netherworld of conspiracy theories, the eyewitness evidence may be fertile territory.

In a pre-trial hearing, defence attorneys accused prosecutors of ignoring a host of witnesses to focus on the "few in the sea of sightings that fit its theory". Those left out include Mr Hunt, who is considered eminently believable by the small group of families now suing the government on the grounds that it had advance warning of a wider bomb plot.

The tug of war over his testimony is beginning to put strain on Mr Hunt. "I've talked to you more than I intended to," he snapped last week, after initially refusing to talk at all. "I don't care whether it's credible to you or anyone else." But other Oklahoma City witnesses are less reticent. Several agree on the fact of a yellow Ryder rental truck moving slowly, as if lost, but put it in different places at the same time. Mike Moroz, a tyre shop manager, also put Mr McVeigh in the company of another man, asking for directions - but this time in the truck rather than in a car following it.

"You want to hear it from the start? All right," said David Snider, a warehouse superintendent, before launching into a story he has told dozens of times. "I'm going to start from A and we'll go all the way to Z. I've put my neck on the line for everybody here. I was raised to tell the truth."

In what seems an elaborate tale, Mr Snider tells of a "verbal confrontation" with Mr McVeigh after he commented on the stranger's haircut. He saw not just two but three vehicles - one speeding away after the blast. A defence investigator has told him, he said, that the FBI did not hand over his statement to them.

One key figure that the government does intend to call worked in the Kansas body shop where Mr McVeigh allegedly rented the truck under a false name. Tom Kessinger remembered "Mr Kling" as a man with "beady eyes" and a horizontal line that ran beneath his jaw. That description, hours after the bombing, was accurate enough to match Mr McVeigh to his real name at a nearby motel where he stayed. But Mr Kessinger will be undoubtedly be quizzed over his description of a second man, with dark eyebrows and a baseball cap.

The lurking figure became the shadowy "John Doe No 2", for months the target of a huge FBI manhunt. But in an attempt to tie up another dangerously loose thread, the bureau finally announced that the description was actually of Todd David Bunting, a soldier who happened to rent a truck the next day.

"We will certainly contend that there is a John Doe 2 and maybe 3, 4 and 5", said Mr McVeigh's lawyer, Stephen Jones - thereby helping to spread the blame away from his client.

It is in the interests of the defence to complicate the picture as much as possible, while the prosecution will be seeking to present as clear and simple a conclusion as it can: that Mr McVeigh is guilty of murder 168 times over, and should pay with his own life. Somewhere between these two strategies the messy truth, as people like Mr Hunt see it, may get a little lost.