The trial of Ireland's biggest ever bank robbery opened in Belfast this week with claims that a bank official forced to take part in the raid was actually the gang's "inside man."

More than $50 million was stolen during the raid on Northern Bank headquarters in Belfast city center on December 20, 2004.

The families of bank employees Chris Ward and Kevin McMullan were held hostage during the raid, while the bank officials were forced to hand over $50 million to robbers waiting outside the bank.

PSNI Chief Constable Hugh Orde claimed the IRA had carried out the robbery. Sinn Fein denied any Republican involvement.

The political fall-out from the robbery was a key factor in unionists refusing to go back into power-sharing government with Republicans for nearly four years.

On Tuesday bank employee Chris Ward went on trial charged with taking part in the robbery.

Prosecution barrister Gordon Kerr claimed Ward had deliberately changed a bank work's rota to ensure that he and supervisor Kevin McMullan were on duty on the day of the raid.

Kerr claimed the facts of the prosecution case would establish that the robbers had "a high degree of inside knowledge" and that it could only have come from Ward. He claimed the evidence excluded any "reasonable possibility of an innocent explanation" on Ward's part.

However, Kerr admitted that the evidence against Ward was circumstantial.

It is understood the main prosecution witness against Ward is McMullan, who is expected to tell the trial that Ward's actions on the day of the robbery were not consistent with someone being forced to act under duress.

Ward denies having played any willing part in the robbery and claims that police are attempting to make him a scapegoat for the robbery.