The High Court in Edinburgh has heard that Elaine Doyle's body was discovered in a lane near her home in Greenock, Inverclyde, more than 27 years ago.
The jury has been told that the 16-year-old girl was covered with a blanket from a police car before being taken to the mortuary.
Retired detective inspector James Goldie, 76, vehemently denied that he had covered Elaine's body.
He said: "I am desperate to tell you I did not at any time cover the body." He also insisted that he had not ordered anyone else to put the cover over Elaine.
Blankets were hung on a fence at the scene, the trial has heard.
Defence QC Donald Findlay described the move as "a humanitarian thought", but added: "That was a potentially catastrophic blunder by police at the scene."
Mr Goldie replied: "I agree with you there."
Mr Findlay continued: "It could have completely blown apart any chance there was of tracking down the real killer of Elaine Doyle."
Mr Goldie was shown a number of statements he made during the long-running murder hunt.
In June 2012 he told detectives who were still making inquiries into the death that he was told residents in a building were looking over the scene in Ardgowan Street. Two men were also approaching the scene in a lane leading to lock-up garages.
Mr Goldie's statement continued: "I told him - it was a young male officer, I don't remember his name - to go to tell the residents to move back into the house. He walked a few yards then turned to say he had some blankets in his panda car so I told him to take them and place them on the garden side to hide the view of the body."
Mr Findlay said the jury would hear "100% guaranteed gold-plated evidence" that a blanket had covered the girl.
He added: "Somebody should have the guts, the honesty, the integrity to come forward and say: 'This was my fault'."
John Docherty, 49, now of Dunoon, denies murder. He claims that at the time he is alleged to have stripped and strangled Elaine Doyle, 16, in a lane in Greenock he was at home with his parents, who are no longer alive.
Mr Docherty has also lodged a special defence of incrimination suggesting the culprit might be among a list of 41 names taken from files of the police investigation into the murder.
Mr Findlay said whatever the motive was, covering the body was a mistake. He said: "Not only might it have removed evidence which might point to the guilty person, it might lead to evidence being brought into the crime scene which pointed to an innocent person."
"Possibly," agreed Mr Goldie.
The murder charge alleges that Mr Docherty forced Elaine to the ground, pushed her face into the ground, sat or knelt on the teenager then placed a ligature round her neck and strangled her.
Mr Docherty also denies stealing a handbag from Ardgowan Street, also on June 2, 1986. He further denies a charge of attacking another woman, Linda Hargie, on various occasions between 1990 and 1995 at an address in Anne Street, Greenock by seizing her and pushing her and punching her on the head. The trial continues.