A retired detective who remains haunted over the Bible John murders believes someone out there knows who the killer is.
On the 50th anniversary of the final murder, Bob Johnstone has appealed for a man identified as Castlemilk John to come forward and unmask who the killer is.
Mr Johnstone told STV News: "Fifty years down the line, I would make an appeal to the man known as Castlemilk John who was actually the friend of the so-called Bible John.
"It may well be after 50 years, he would be able to come forward, even to see me personally and throw some light on this horrendous inquiry."
Bible John was the nickname given to a suspected serial killer blamed for the deaths of three women in Glasgow in the late 1960s.
Patricia Docker, 25, Jemima McDonald, 32, and Helen Puttock, 29, all died after nights out at the city's Barrowland Ballroom. All three had been raped and strangled.
The known movements and modus operandi of convicted serial killer and rapist Peter Tobin have given rise to suspicions that he may be Bible John.
Mr Johnson, who reached detective superintendent before retiring in 1991, was involved with 55 murder cases while in charge of the CID in Glasgow.
He said all but one came to a satisfactory conclusion - the Bible John murders.
The body of final victim Mrs Puttock was discovered by a dog walker behind a tenement in Scotstoun on October 31, 1969.
Mr Johnson said he is reminded of the murders every October, adding: "Another year gone and we still haven't found a solution to this."
Mrs Puttock had been on a night out to the Barrowland Ballroom with her sister, Jean Langford, where they met two men called John.
One said he was from Castlemilk and worked as a slater.
He later walked to George Square to get a bus home, leaving the sisters and the killer to hail a taxi.
Mrs Langford was dropped off in Knightswood, with the taxi continuing towards Mrs Puttock's Scotstoun residence.
She never saw her sister again.
Mr Johnson said Joe Beattie, the detective superintendent in charge of the murder investigation, spent the "best part of his life trying to get to the bottom of the inquiry".
He explained that the police team didn't have the advantage of DNA testing at the time, which would have made a "tremendous difference".
However, he believes Castlemilk John is still out there with knowledge of who the murderer is.
He said: "He's probably mentioned it to someone, even someone in his family he may have mentioned it.
"I'd be quite happy to hear from them.
"Nowadays people have got a different attitude to things in life and it may well be this person would come forward, the Castlemilk fellow.
"It may well be [Bible John's] pal is now dead, which would save a lot of anxiety among different people involved in the inquiry."