Intelligence agents of the British army and police helped Protestant extremists kill Catholics in the late 1980s, including a lawyer well-known for defending IRA suspects, a four-year official investigation concluded Thursday.

Sir John Stevens, commander of London's Metropolitan Police, said he documented widespread collusion in Belfast between the outlawed Ulster Defense Association and officers from the police Special Branch and the army's Force Research Unit.

Both units, Stevens said, had agents within all of Northern Ireland's outlawed paramilitary groups in hopes of preventing some killings. But, in what he called "a disaster" for the rule of law, they encouraged other attacks to go ahead.

Stevens' findings proved shocking and divisive at a moment when the British and Irish governments are pressing for a breakthrough in Northern Ireland peacemaking.

British-Irish plans for driving forward the province's 1998 peace accord have been postponed as government negotiators try to persuade the Irish Republican Army to disarm fully and its allied Sinn Fein party to accept the legitimacy of the police force.

But Stevens' report confirmed for many Catholics their long-held suspicions that law enforcement agencies had directed Protestant killers. His 30-strong team of detectives investigated suspected collusion in 26 murders mostly in the late 1980s.

Stevens said moles within the Ulster Defense Association had been encouraged "to commit criminal acts and get involved in murders," among them the killing of attorney Pat Finucane.

The security forces' knowledge of plans to attack Finucane meant it "could have been prevented," Stevens said.

Finucane, 38, who had three brothers in the IRA and specialized in defending IRA members, was shot by two UDA gunmen as he sat down to dinner with his wife and children in February 1989. He was the first lawyer slain in the 35-year conflict over this British territory that has claimed more than 3,600 lives.

UDA members "were given information and equipped with weapons and directed towards targets that the British government wanted out of the way," said Michael Finucane, one of the victim's sons and also a lawyer.

Stevens, who has led three probes of collusion in Northern Ireland since 1989, told reporters that the collusion with terrorists "was systemic" in the late 1980s within the army's Force Research Unit.

He said Special Branch officers were paying at least two Belfast UDA members for tipoffs and other information. But Stevens's 20-page summary didn't name any collusion suspects.

A previous Stevens-led probe exposed the army unit's senior agent in the UDA, Brian Nelson. His job within the UDA was to identify targets and research means of killing them.

Nelson, convicted in 1992 on five counts of conspiracy to murder, was paroled in 1997 and died last Friday of a brain hemorrhage.

Stevens said Nelson's tipoffs prevented two UDA attacks, one of them aimed at Sinn Fein party leader Gerry Adams. But he said many secrets must have died with Nelson.