The fleeting chance encounter almost 28 years ago was recalled at the High Court in Edinburgh yesterday by reformed heroin addict Martin Brown, 52.
He told how detectives visited him at his London home in September 2012 to see if he could pick out the man he saw in a dozen photos he was shown.
The jury heard it was the day of the first matches in the Mexico World Cup. Mr Brown, who had moved to London, had returned to Greenock to visit his parents.
He was around Ardgowan Street and Ardgowan Square when he saw a girl he thought to be around 20 walking there but did not see the man at first.
"I glanced up the second time and that is when I saw someone walking behind her. He seemed to be walking faster as if he was trying to catch up."
Advocate depute John Scullion, prosecuting, asked Mr Brown what the man was wearing. "Dark clothing, I remember," answered Mr Brown. He saw his face "for a split second," he added.
Mr Brown said the man had "big eyes" and added: "There was something strange-looking that made me want to look away and go home.
Mr Scullion asked if the man had an angry expression and Mr Brown told him: "In retrospect, yes."
He was giving evidence at the trial of John Docherty, 49, of Dunoon, who denies murder. Defence QC Donald Findlay pointed out that much of the description Mr Brown had given of the girl he saw did not match Elaine.
The trial continues.