A former IRA volunteer, he turned against the IRA and other republicans in the most open and public of ways, developing his own brand of "naming and shaming" alleged activists and relentlessly criticising republicanism.
He was not unique in doing so, since recent years have produced up to half-a-dozen former IRA members who have now forsworn violence and who regularly criticise the IRA and Sinn Fein in the media and in books of memoirs.
But he was remarkable in that he returned to live openly in a hardline republican area in Newry, a town which holds hundreds of IRA members and supporters and thousands of Sinn Fein voters. Many former prisoners and activists live within a 10-mile radius of his home, and all of them detested him for his behaviour and regarded his presence as a standing affront.
Mr Collins, 44, was constantly intimidated and abused, suffering a number of attacks. With hindsight, perhaps the surprise lies not in his death but in the fact that he stayed alive for as long as he did.
His body was found at 6am yesterday on a country road a few hundred yards from the house where he lived for the past two years. He had suffered severe head injuries.
Although the IRA is assumed to be the prime suspect for his death, the Sinn Fein president, Gerry Adams, said yesterday afternoon that he had no reason to think foul play was involved. If there was foul play, he added, "then of course it's wrong".
The security forces and the Government will now be keenly searching for confirmation of mainstream IRA involvement, since there is already heated criticism of the organisation for its continuing use of violence in the form of "punishment" shootings and beatings.
If the IRA was responsible the timing of the killing is difficult to fathom, given this background and given the Commons debate on prison releases which took place yesterday.
Martin McGartland, a one-time informer who lives at a secret address in England, said: "There is no doubt that this has got something to do with the IRA or one of its so-called splinter groups.
"I thought the IRA were sincere about their ceasefire. This murder shows that the IRA will never forget anyone who has double-crossed them or gone against their organisation."
There are other possibilities. Last year, Mr Collins made a particular denunciation of the Real IRA, the breakaway group which carried out the Omagh bombing in August. In a lengthy newspaper article he all but named the Real IRA's alleged leader, claiming he had also been responsible for the killing of 18 soldiers at Warrenpoint in 1979.
There is also the possibility that the attack on Mr Collins was carried out by republicans on what might be called an unofficial or semi-official basis.
Last year, in an open letter to Mr Adams complaining of intimidation, Mr Collins wrote: "The people that are carrying this out are former Provisionals, former Sinn Fein people, and are now playing dual roles of being tied in with Sinn Fein, tied in with the republicans and tied in with the dissidents."
During his IRA career Mr Collins was clearly a valuable asset to the terrorist organisation, being involved in at least five murders and possibly 15. From the late 1970s until the mid-1980s he functioned as an intelligence officer, helping to gather information through his job as a Customs officer in the Newry area.
In 1985, he cracked under RUC interrogation and made confessions which led to him being charged with five murders. He also initially agreed to act as a "supergrass", promising to go into court to give evidence against alleged former associates.
But afterwards he refused to testify and disowned his own statements. He was acquitted by a judge who accepted his claims that the RUC had used unacceptable methods to extract his alleged "confessions".
At that point, Mr Collins disappeared from the scene for almost a decade before reappearing on a television programme to speak about the killings. In doing so, he relied on the legal provision that, having been tried and acquitted, he could not be prosecuted for them again.
One of the deaths was that of an 11-year-old Protestant schoolboy who died when a bomb went off in the Co Down town of Banbridge. He said he had "scouted in" the bomb. Another was that of Ivan Toombs, a Customs service official who was also a part-time member of the Ulster Defence Regiment.
In the 1997 book Killing Rage, Mr Collins described in detail how he carried out the surveillance and planning involved in the Toombs killing and other murders.
He wrote: "When I set out to kill Ivan Toombs I was setting out to kill a UDR uniform. What was brought home to me was that you can never kill a uniform, you can only kill a person ...
"By exposing myself to the anger of my former comrades and the families of my victims, I wanted to show that I had thought long and hard about what had happened and that it is possible to become a different person - as we all have to become different people if we are to live together in Northern Ireland without political violence.
"I truly believe that only by confronting our past actions, by understanding the forces which drove us to carry them out, can we hope to create the possibility of a society in which these actions do not occur again."
His return to Newry appears to have been part of a personal odyssey undertaken to grapple with his conscience and come to terms with his past. This led him not to introspection but to broadcast his thoughts and contribute long articles to newspapers.
In 1998 he accepted payment from the Sunday Times for appearing as a witness in a libel case in Dublin. He told the court that the plaintiff was a senior member of the IRA. His high profile in the media continued despite intimidation which included being struck by a car in a hit-and- run incident and a serious fire at the family home he was renovating.
Last year, he said he was leaving Newry with his wife and children, but at another level it seems he wished to stay and continue his intense self-analysis. He asked at the time, with terrible prescience: "What's the next stage? Does my house get burnt? Do I get executed on the street?"