A former senior RUC officer has spoken for the first time about his unlikely friendship with Pat Finucane, the solicitor shot dead by loyalists amidst allegations of security force collusion.

Kevin Sheehy, who was variously head of the serious crime, anti-racketeering, and drugs squads, has disclosed how his friendship with Finucane was cemented when they were students at Trinity College, sharing digs, and playing for the university football team.

"Pat held strong republican views and when I said I was considering a career in the RUC, we agreed to differ. But even after I joined, we remained good friends. We'd bump into each other in the courts and go for coffee or a pint of Guinness," he told the Sunday Tribune.

Sheehy writes at length about the friendship in his autobiography, More questions than answers: reflections on a life in the RUC, which is published tomorrow. He also covers his involvement in the 1979 Warrenpoint bomb investigation in which 18 British soldiers were killed by the IRA.

The bomb was detonated from a field across Carlingford Lough in the Republic but Sheehy claims that Charlie Haughey later ordered gardaí not to co-operate with the RUC investigation because the soldiers were members of the Parachute Regiment which had shot dead 14 unarmed civilians on Bloody Sunday.

Sheehy, who came from a working-class North Belfast family, was the first Catholic graduate to join the RUC. He first met Pat Finucane when they attended St Malachy's College in Belfast. Bik McFarland, who went onto become officer commanding the IRA prisoners during the 1981 hunger-strike, was also a pupil.

Sheehy studied history and politics at Trinity while Finucane studied law. "We shared a house in Rathmines with other lads from Northern Ireland. I was always unionist and had a picture of the Queen on my bedroom wall which Pat and the others slagged me about.

"At the cinema, I'd try to escape before the 'Soldiers' Song' was played, and they'd block me in for the craic.

"I actually courted Pat's future wife Geraldine for a while, though I was fonder of her than she was of me. I later introduced her to Pat and she fell for him. Until he died, my partner Rosalind and I would regularly have dinner with Pat and Geraldine in their home in Belfast. Pat and I would argue about politics over a drink. There would be voices raised as we both had strong opinions but we always parted on good terms."

Sheehy said that shortly before he was shot dead by the UDA in 1989, Finucane was concerned about his security and approached him about obtaining a legally held gun: "I advised him on how to go about it."

Finucane was shot dead in front of his wife and children as he ate Sunday dinner. An officer at the murder scene, knowing of the pair's friendship, phoned Sheehy. "I went to the house. There were dozens of mourners there. Some looked at me in disbelief. Geraldine had been shot in the foot. We embraced. She said: 'Thanks for coming but it might be better if you didn't stay.' I didn't go to the funeral because I didn't want there to be a confrontation with anyone."

Sheehy doesn't believe there was collusion in Finucane's murder nor does he support a public inquiry into the shooting: "But I feel for the family and I think steps should be taken by the authorities to give them the answers they crave."

Sheehy remembers the surreal scene after the 1979 Warrenpoint bomb: "Mutilated and burnt bodies lay scattered over a beautiful and tranquil landscape. A helicopter was needed to dislodge the soldiers' arms and legs from the trees."

Gardaí arrested, and then released, two men on a motorbike in Omeath, several miles from the detonation point. They also had forensic evidence from the scene, including lemonade bottles and cigarette butts apparently left by the bombers. But RUC requests that the two men be re-arrested were rejected, Sheehy claims: "At a meeting in January 1980, senior garda officers said they'd been instructed by Charlie Haughey to treat the deaths at Warrenpoint as political because of Bloody Sunday and not to help the RUC. This caused much ill-feeling, especially since we'd always enjoyed an excellent relationship with gardaí."

Sheehy's wide-ranging career included interviewing paedophile priest, Father Brendan Smyth, in 1994: "I questioned him about indecent fondling of a seven-year-old. He replied, 'She didn't tell me to stop, she didn't say she didn't want it.'"

Sheehy took early retirement from the RUC in 2001. Before he left, he was interviewed under caution about allegations that he and others were involved in drug trafficking and criminal acts. He was exonerated. He now runs an animal shelter.

'More Questions than Answers: Reflections on a Life in the RUC', Gill & MacMillan €22.99