Prosecutors in the US say a man who helped bomb a government building in Oklahoma in 1995 is guilty of the murder of over 160 civilians.
The attack was one of the deadliest on US soil in peacetime
Terry Nichols, whose accomplice Timothy McVeigh was executed for planting the bomb, is already serving life in prison for planning the attack.
"These two were partners, and their business was terrorism," said a prosecutor, opening Nichols' trial.
Nichols will face the death penalty if the court finds him guilty.
'Guiltier than McVeigh'
Legal experts say he is being tried again because many felt the original life sentence against him was too lenient.
Nichols was found guilty of conspiracy to bomb the Alfred P Murrah federal building in Oklahoma and for the manslaughter of eight security officers in the subsequent blast.
But a total of 168 people died that day, not including the unborn child of a pregnant woman whom prosecutors also say must be added to the tally of victims.
Nichols' accomplice, white supremacist Timothy McVeigh, was executed in June 2001 for driving an explosives-laden lorry to the building and detonating it.
Lou Keel, an Oklahoma State attorney, said Nichols had "more to do with gathering the various components of the bomb than did Timothy McVeigh".
Prosecutors have gathered more than 400 witnesses for the trial, which is expected to take four to six months.
Before opening statements were read out, the judge criticised prosecutors for a delay in notifying the court that a member of their team was related to a number of people on the jury.
Those jury members were dismissed, with warnings from the judge that the case could be thrown out.
Roughly 150 prospective jurors applied to sit on the trial at a courtroom in the town of McAlester, Oklahoma, after the trial was moved there from Oklahoma City because of the difficulty of finding impartial jurors there.
Nichols' defence team had earlier unsuccessfully tried to get the start of the trial postponed so that it could wait for an FBI review into its own investigation of the bomb.
They say they have uncovered a
wider conspiracy behind the bombing, for which Nichols is merely the scapegoat.
But the prosecution hopes to ensure Nichols never successfully appeals against his conviction and gains his freedom.