Police who dragged a car from a waterway in Cambridgeshire confirmed that the badly decomposed remains were Mr Curran's. He vanished in March 1995, two days after being suspended for smuggling toiletries into the prison.
There has been speculation - but no evidence - since his disappearance that he may have been involved in the attempted breakout by five IRA prisoners and a convicted robber from Whitemoor in September 1994. However, sources close to the jail say they suspect Mr Curran, 38, had been acting as a courier for an outside drugs gang.
The car was pulled from a deep man-made dike Chatteris. A Home Office pathologist conducted a post-mortem examination yesterday and confirmed that the remains were those of the prison officer.
Mr Curran is the second Whitemoor officer within a month to be found drowned in such a manner. Marcia Whitehurst, 37, was killed when her car plunged into a river near Wisbech after giving evidence at the trial of the Whitemoor escapers. The police described her death as a "tragic accident".
Prison sources are not the only people who believe third parties may have been involved in Mr Curran's death. In the days before he disappeared he told his wife, Christine, that he was afraid because of something he had done at the jail. Then, on a Sunday, he "popped out" without a coat and never came back.
In an interview earlier this month with the Fenland Citizen newspaper, Mrs Curran said she believed he went out to meet someone and suggested his disappearance had something to do with his job. He told her about supplying the toiletries but "hinted there was something else". Last night, she told the BBC: "I don't believe this was just a road-traffic accident ... I think as I did before that something else was going on here. It is one accident too many."
Mrs Curran said she believed her husband was about to "blow the whistle" - a belief that tallies with prison officers' opinions. One source said: "They had him for the toiletries, but they believed there was alcohol involved and possibly worse. They believed he was prepared to give a statement, but that could be what got him killed."
Mark Freeman of the Prison Officers' Association, said staff at the jail had been outraged by allegations made by Michael Mansfield QC, who represented one of the IRA prisoners, that staff had colluded with the escapees. "A police investigation is being carried out and they will no doubt examine the links between the two deaths of the officers. But it is far too early to say what this may be," he said.