The father of murdered loyalist leader Billy Wright has said he will challenge the report of an inquiry into his son's murder if it does not find there was state collusion in the killing.

Billy Wright, who is believed to have been responsible for up to 30 murders, was shot dead by the INLA in the Maze prison in 1997. The 700-page report into his death will be published on Tuesday.

His father is "100% certain" there was collusion between the INLA killers and the authorities.

"My son wasn't a choirboy. He was a UVF man. Had he been shot dead by republicans on the street, I wouldn't like it but I'd accept it. But the INLA didn't act alone. There was official collusion," David Wright told the Sunday Tribune. "Billy was killed in jail while in the care of the state. It was no accident. He was a roadblock to the political process at the time and they were determined to remove him."

The £30 million (€36m) inquiry was chaired by Lord MacLean.

David Wright, who has always opposed paramilitary violence, said: "I'm not out to change anybody's mind about Billy. I'm interested only in the truth. If the inquiry tells the truth, I will welcome it. If it doesn't, I will challenge it however I can.

"I've been up against the political establishment from the beginning. My son was the last person in Northern Ireland to be executed at her majesty's pleasure."

Billy Wright, 37, the UVF's Mid-Ulster leader known as 'King Rat', opposed the peace process which was endorsed by the Belfast-based UVF leadership. He then formed the breakaway Loyalist Volunteer Force. He was shot dead in a prison van, heading to a visit.

There was a series of 'coincidental' security lapses at the time: the prison authorities gave the INLA a copy of the LVF visit list the night before the murder, the first and only recorded instance of such a 'mistake'; a crucial security camera was not working; and a prison officer in the watch-tower overlooking the murder scene was stood down.

Questions also centre on how the INLA was able to smuggle weapons into the jail and how the team of killers was able to cut through a wire fence to reach the prison van.