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British Prime Minister David Cameron on Wednesday condemned actions by British agents in the 1989 death of a Belfast lawyer, one of the most bitterly disputed killings of the entire Northern Ireland conflict.

Cameron cited a long-awaited report on the slaying that said there was a shocking level of state collusion with an outlawed Protestant group in the murder of Pat Finucane, who specialized in defending Irish Republican Army suspects.

Two gunmen from the Ulster Defense Association shot him more than a dozen times in his Belfast home as he was having Sunday lunch with his wife and three children. Employees of the state and state agents played "key roles" in the murder, the report says.

"It cannot be argued that these were rogue agents," Cameron said. However, he declined to order an inquiry, saying that more was learned from the report by human rights lawyer Desmond de Silva than would have been gained through a public inquiry.

Previous investigations already have confirmed that both the British army and the anti-terrorist unit of Northern Ireland's police had agents and informers inside the Ulster Defense Association involved in the killing.

Cameron said de Silva concluded that Finucane probably would not have been killed were it not for the actions of British agents in the Ulster Defense Association.

"Sir Desmond is satisfied there was not an overarching state conspiracy to murder Patrick Finucane," Cameron said. "But while he rejects any state conspiracy he does find, quite frankly, shocking levels of state collusion."

Finucane specialized in defending Irish Republican Army suspects and had three brothers in the outlawed group. Two gunmen from an enemy paramilitary group, the Ulster Defense Association, shot him 14 times in front of his wife and children as they ate a meal in their Belfast home.

A series of secrecy-shrouded probes led by former London police commissioner John Stevens has already concluded that Belfast police and British army intelligence units both operated UDA agents involved in the attack. Stevens says his probes produced 9,256 written statements, 10,391 documents exceeding 1 million pages, and 16,194 exhibits of potential evidence -- virtually none of it made public, all of it open for de Silva to examine.

De Silva's report shed new light on the role that Northern Ireland's legal forces of law and order played in influencing the UDA, a working-class Protestant gang committed to terrorizing the Catholic minority. But his findings may not spur new prosecutions, in part, because key UDA players are already convicted or dead.

One police informer, senior UDA gunman Ken Barrett, pleaded guilty to killing Finucane and received a life sentence in 2004. He was paroled two years later under terms of Northern Ireland's peace accord, which offered early freedom for all convicted members of paramilitary groups observing cease-fires.

Another UDA man on the police payroll, William Stobie, was killed by UDA colleagues in 2001 after testifying he may have supplied the guns used for the Finucane hit and tried to tip off police handlers about it.

A British army intelligence agent, Brian Nelson, served as the UDA's top intelligence officer -- responsible for researching and picking targets -- in the late 1980s. Nelson in 1992 pleaded guilty to 20 criminal charges, including conspiracy to murder, but not directly to involvement in the Finucane killing. He was paroled in 1997 and died in 2003.

The UDA killed more than 250 people, mostly Catholic civilians, before calling a 1994 cease-fire, renouncing violence in 2007, and disarming in 2010.

In October 2011, Britain appointed de Silva, a human rights lawyer, to review its largely secret documentation on the Finucane killing.