An off-duty detective who discovered the bodies of Lesley Howell and Trevor Buchanan in a fume-filled garage raised concerns with investigating officers that their deaths were not suicide.
David Green told Coleraine Courthouse yesterday he had suspicions that dentist Colin Howell, who 18 years later confessed to their murders, may have been involved.
Despite his reservations, the original police investigation in 1991 concluded that the pair had taken their own lives in a bizarre suicide pact.
That finding was based in part on the evidence of Howell and his lover Hazel Stewart, Mr Buchanan's wife, who is now standing trial for the double murder.
They told detectives they believed their partners killed themselves because they could not come to terms with their affair -- when in actual fact they had been murdered.
Mr Green was a member of the same church as the Howells and Buchanans and on the day after their murder, church elder James Flanagan approached him and said Colin Howell was worried because his wife and Mr Buchanan, also a policeman, had gone missing.
Mr Flanagan had gone to check a house in Castlerock earlier that morning at the dentist's request but had found nothing.
Mr Flanagan went with Mr Green to take another look and this time Mr Green made the grim discovery in the garage of the house. Mr Buchanan's body was slumped in the driver's seat of a car and Mrs Howell was lying dead in the boot surrounded by family pictures with earphones in her ears.
Mr Green, an experienced detective who at that time had been in the police for 17 years, said something told him it was not a simple suicide.
Giving evidence in the trial of Stewart, the now retired officer said he was very suspicious about how he found the bodies.
He told the court he voiced his concerns with three senior detectives from Coleraine who were working on the case.
After pleading guilty to the murders in November last year, Howell will appear as a witness against Mrs Stewart during this trial.
Howell said he resumed a sexual relationship with Mrs Stewart weeks after the funerals of their spouses and continued it for five years, at first secretly but by 1994 he said he was taking his children round to her house and that they had gone on holidays to Newcastle, Co Down, and the Lake District. He said he proposed to her in 1995 and went to view two dentistry practices in Scotland with a view to resettling both their families across the Irish Sea. "She didn't want that," said Mr Murphy.
Their relationship ended in 1996 when Mrs Stewart began seeing another man, Trevor McAuley.
Mr Murphy said there was no doubt she had engaged in a joint enterprise to kill Mrs Howell and Mr Buchanan.
"The purpose was to rid them of their partners so they could be together," he said.
"She had to ensure that he was sedated and asleep before Howell arrived," he said. "She did that to facilitate the plan."
"She led him in and she saw what he was doing, she prepared clothes to be put on her dead husband."
He added that Mrs Stewart was an "accomplished liar" who had perpetuated the myth that her husband killed himself for almost two decades.