Timothy McVeigh, and his friend Terry Nichols are charged with murder and conspiracy in connection with the bomb which killed 168 people in Oklahoma a year ago. Mr Snyder's account, delivered to the FBI, might seem like damning prosecution evidence, but Mr McVeigh's lawyer, Stephen Jones, sees it as doing the opposite - helping to undermine the prosecution case.
If Mr McVeigh was the passenger, Mr Jones argues, who was driving the truck, which contained 5,000lb of home-made explosives primed for the worst act of mass murder in US history? Mr McVeigh's former army buddy and alleged co-conspirator, the only other person charged, Mr Nichols, was - even prosecutors accept - 300 miles away at home in Kansas.
Mr Snyder got his sister to draw a kind of photofit of the man he describes as having "a pretty good tan ... olive-coloured skin," and "a thin pencil moustache like in the old gangster movies". The driver is certainly not Mr Nichols. And despite the word of many such witnesses who insist Mr McVeigh was not alone in the truck, the FBI has issued no current wanted posters for anyone still being sought for the bombing. Far from being the bombing mastermind, was Mr McVeigh therefore a mere footsoldier in a bigger conspiracy?
With political pressure from President Bill Clinton to secure the death penalty, agents and prosecutors refuse to talk publicly. This is the most complex case in US criminal history - 22,000 witnesses have been interviewed. But there are numerous inconsistencies and unanswered questions. At least one witness claims he saw a getaway car driving behind the truck as it progressed through central Oklahoma City. And then there was "John Doe Number Two", apparently seen when Mr McVeigh rented the truck, but never found.
Taken together, Mr Jones believes, such statements point to a prosecution case which is weak and circumstantial. "The ... bombing had to be a large conspiracy," he said, scoffing at the idea that Messrs McVeigh and Nichols alone could build and deliver such a bomb. "Terrorism," Mr Jones says, "requires an infrastructure."
Oklahomans, still grieving, regard such views as fantasies, but many also suspect that, in their determination to nail the two accused, prosecutors are ignoring evidence of a wider conspiracy.
There are fears that other bomb plotters may still be on the loose. The McVeigh-Nichols trial is unlikely to begin until next year and the burden on federal prosecutors is heavy.
They must either expose this suspected wider conspiracy or prove that two drifters are the most accomplished terrorists of our times.
Gavin Esler's Newsnight report is on BBC2 at 10.30pm tonight