Witness Colin McIntyre, 44, told a court that he had been terrified by threats of violence from officers who did not believe he was at home with his family watching television on the night the teenager died.
"The police were bullying me into making a confession," he said, recalling the interview days after 16-year-old Elaine's body was found near her Greenock home.
"They tried to blame me for it."
Defence QC Donald Findlay suggested the statement shown to the court was either a sick joke by an attention-seeking teenager - or a true confession by someone who was at the scene of the murder.
The lawyer asked why Mr McIntyre thought officers should put their careers and pensions on the line by fabricating a story.
He replied: "I think about it a lot and I don't know why."
Elaine was found naked and strangled early on June 2, 1986. She hadn't returned from a disco at the Celtic Club, in the town's Laird Street.
Mr McIntyre, then 16, had a part-time job in the Shamrock Club - another Celtic supporters' club in Greenock.
Police visited him there on June 7 and he told them where he had been the previous Sunday.
The High Court in Edinburgh heard that later that day Mr McIntyre had appar-ently made another statement.
John Scullion, prosecuting, read what was supposed to be a graphic account of Elaine's death.
He repeatedly asked Mr McIntyre: "Is that information accur-ate?" Mr McIntyre told him each time: "No, it all came from the police."
The statement told how Mr McIntyre had left his home in John Street, met three pals in the town centre and had also met Elaine. The four youths walked her home and all went down a lane off Ardgowan Street - where the girl's body was found.
As they talked, one of Mr McIntyre's friends began kissing Elaine and taking her clothes off.
The four youths gathered round her as she started to struggle.
The statement said that the youths were planning group sex but that Elaine did not want it to happen.
On trial is John Docherty, 49, of Dunoon, who denies murder and claims that at the time he is alleged to have strangled Elaine, he was with his parents.
Docherty also claims the culprit might be among a list of 41 names.
The trial continues.