Twenty-nine year-old Michael Fortier knew in advance about the bombing, the worst incident of its kind ever to take place on American soil.

168 people died in the blast which destroyed one of the city's federal buildings three years ago.

'I'm so completely ashamed'

Fortier was a close friend of the conspirators, Timothy McVeigh and Terry Nichols, from his days in the army.

Judge G Thomas Van Bebber heard pleas from both sides

During the trial, he admitted that he could have stopped the atrocity. He also admitted that he sold stolen weapons to finance the bombing and that he lied to FBI investigators.

Fortier told the court that his actions and inaction had hurt many people - he was sorry and asked for forgiveness.

"I am so completely ashamed that I did not come forward with my knowledge right away," he said before learning his sentence.

He said he never thought Timothy McVeigh's plot "would bear such rotten fruit."

Survivors demand toughest penalty

70 survivors and relatives attended the hearing with 16 victims testifying about how the bombing had changed their lives.

Dorothy Hill, who was injured in the blast said: "I suffer from guilt. Horrible, horrible guilt for being alive while so many others died, especially the children."

Another victim described Fortier as a "despicable man" who had maintained his misplaced loyalty to his "vicious colleagues.

"He chose to let people die," said Diane Leonard, who lost her husband in the blast.

"Mr Fortier had knowledge of the crime and chose to remain silent and allow 168 innocent people to die, hundreds more to be physically injured and thousands to be emotionally scarred."

Many urged the judge to sentence Fortier to 17 and a half years in jail, the maximum prison term.

Lawyers urge leniency

Fortier's lawyers argued that he should be treated leniently because his evidence helped to convict the men who carried out the bombing.

They described him as the "mailman who delivered the evidence" which convinced jurors that McVeigh and Nichols were guilty of conspiracy to murder.

They also pointed out that he had co-operated fully when the first cases came to trial.

Despite the pleas, US District Judge G Thomas Van Bebber imposed a 12-year sentence, fined Fortier $200,000 and ordered him to repay an Arkansas gun dealer whose weapons were stolen to pay for the bombing.

Fortier's attorney said he would appeal against the sentence.