A trial heard how Allan Cleary, 46, asked a pal to give him a false alibi, when officers investigating the teenager's death questioned clubbers in Greenock.
Mr Cleary, a sales assistant in an electrical shop at the time, admitted in court yesterday he had made "a terrible error of judgement."
Trying to explain it, he said he had been worried about walking the streets alone for a time on the night when Elaine, 16, is thought to have been stripped and strangled. Her body was found near her home on June 2, 1986.
On trial is John Docherty, who denies murder. The 49-year-old's lawyers have drawn up a list of 41 possible suspects which, it is claimed, might include the real killer. The false statements made by Mr Cleary years ago have added him to the list.
The trial heard Mr Cleary met Elaine when he went to the Judy Plum jeweller's - where she was an assistant on a YTS scheme - to buy an earring.
Mr Cleary told detectives at the time he had seen her in the early hours of June 2 at a hamburger stall in the town centre. But the claimed sighting was not true because, it is thought, Elaine was already dead.
Defence QC Donald Findlay suggested there might be an "ulterior motive" for telling "a detailed cocktail of lies." The lawyer asked: " Do you now want to admit to the murder of Elaine Doyle?"
Mr Cleary replied: "No, because I had nothing to do with it."
The trial continues.