William Stobie: Self-confessed UDA quartermaster
Stobie, 51, who had been accused over the murder of solicitor Pat Finucane, was shot dead at about 0615 GMT on Wednesday.
The murder of Mr Finucane, a high profile Catholic lawyer, was one of the most controversial killings in recent times in Northern Ireland, and prompted allegations of police collusion.
Stobie was shot several times at close range as he walked from his home on the Forthriver Road to his car. It happened outside a block of flats in the Glencairn area of the city. He died at the scene.
The attack came just 10 days after police warned Stobie, a self-confessed former Ulster Defence Association quartermaster, about his personal security.
Northern Ireland Chief Constable Sir Ronnie Flanagan said: "There was information that Mr Stobie may have been under threat and we did visit Mr Stobie to alert him to that threat and we gave certain advice to him".
The Red Hand Defenders, admitted the killing, and said Stobie had been shot because of "crimes against the loyalist community".
The RHD is a cover name used in the past by the UDA/UFF and the Loyalist Volunteer Force.
Detective Superintendent John Brannigan, of the Police Service of Northern Ireland, said members of the UFF were most likely to blame for the "brutal murder callously carried out by thugs."
"We believe that loyalist paramilitaries are responsible and our information would point to the UFF," he added.
Last month the case against Stobie, who was accused of aiding and abetting the killing of Pat Finucane, was dismissed through lack of evidence.
Mr Finucane was shot dead in front of his family at his home in 1989, in a killing admitted by the UDA/UFF.
A team of detectives, headed by Metropolitan Police Commissioner Sir John Stevens, has been investigating Mr Finucane's murder and claims of security force collusion with loyalists.
Sunday Tribune journalist Ed Moloney interviewed Stobie 11 years ago and successfully fought police legal action to make him hand over his notes to the Stevens Inquiry team.
"The UDA killed this man," Mr Moloney told BBC Radio Ulster.
"He was in fear of the UDA, and it seems that his fears and the warning from the police were all too real."
Police confirmed later on Wednesday that officers warned Stobie about his personal security on 2 December.
It is believed the threat had come from loyalist paramilitaries.
Leading loyalist John White said he was certain the UFF murdered Stobie.
"I don't think it was republicans and if loyalists are involved then I would be absolutely certain that it was that organisation, given it was that organisation that he was a member of," he said.
"Unfortunately when one joins an organisation like that it is pointed out to them very clearly that the penalty for such activities is death."
Mr Finucane's family expressed shock at Mr Stobie's killing.
They said: "The family did not want him murdered nor did they even want him prosecuted. All they wanted was the truth.
"If a public inquiry had been established into Pat's murder instead of the Stevens police investigation, Billy Stobie could have been granted anonymity and his identity unknown and he would probably still be alive today."
Northern Ireland Security Minister Jane Kennedy condemned the murder.