DUBLIN — A Protestant paramilitary leader and police informant from Belfast pleaded guilty to more than 200 terrorist crimes on Friday, including five murders. The plea was the first step in a legal process that could expose past collusion between the police and loyalist terrorists in Northern Ireland during the years of sectarian conflict known as the Troubles.

Gary Haggarty, 45, a former leader of the Ulster Volunteer Force in the Mount Vernon area of Belfast, appeared in Laganside Court on Friday to enter his plea, which covered crimes committed from 1991 to 2007. He has been cooperating with the police for more than seven years, the authorities said, giving 1,100 interviews whose transcripts run to 23,000 pages. During this period, he is believed to have been living in southern England.

The five murders — of four Catholic men and one Protestant man, who was handcuffed to a railing and beaten to death — each carry a life sentence. But the court is expected to reduce Mr. Haggarty’s prison time significantly if he provides testimony against other members of his group and about any collusion between the group and officers of the counterterrorist Special Branch of the province’s former police force, the Royal Ulster Constabulary.

He is scheduled to appear in court for sentencing in September, when the judge will establish the minimum number of years he must serve of his life sentences. It is possible that, having already spent some time in custody, he could walk free.