The infamous Bible John murders are still unsolved half a century on but the case remains open, Police Scotland has said.

Taking place in the late 1960s, the three killings sparked a decades-long manhunt to trace the murderer who would become known as Bible John.

Friday marks the 50th anniversary of the discovery of the first murder victim, 25-year-old nurse Patricia Docker, on February 23, 1968.

The serial killer is also believed to have murdered Jemima McDonald, 32, found dead on August 15, 1969, and 29-year-old Helen Puttock, discovered on October 31 that year.

All three of the women were found raped and strangled with their handbags stolen, and all three had gone to the Barrowland ballroom on the night they died.

More than 100 detectives worked on the case to try and track down Bible John, taking more than 50,000 statements in door-to-door enquiries.

However, the only witness to ever have said they had encountered the killer, Jean McLachlan, died aged 74 in 2010.

It was Ms McLachlan, sister of victim Ms Puttock, who provided the suspect's description as a well-dressed young man, tall, slim, with reddish or fair hair, who was polite and well-spoken.

She said the stranger had given his name as "John Templeton" or "Sempleson" and that he had frequently quoted from the bible during the taxi ride home, which was the basis for his nickname.

Ms McLachlan's description of Bible John led to one of the first uses of a widely-shared identikit image produced by police, which became one of the most famous portraits in Scotland.

Despite the trail being long cold, police say they regularly review such cases in line with "advances in technology and investigative approaches".

Detective chief inspector Mark Bell said: "The passage of time is no barrier to the investigation of unresolved murder cases, and in the view of Police Scotland these cases are never closed.

"Homicide Governance and Review actively keeps all unsolved and unresolved homicides under review and meets regularly with the Crown Office and Procurator Fiscal Service in an attempt to review these cases and pursue resolution.

"Police Scotland, along with our partners in the Scottish Police Authority forensic services, continue to relentlessly pursue advances in technology and investigative approaches which help bring those responsible for serious and violent crimes to justice and provide answers for families of the victims of such crimes.

"Scientific and forensic developments, combined with information from the public and determined investigative work can yield new opportunities in such cases."

He added: "In addition, given the passage of time, personal circumstances and associations can change.

"If anyone has any new information that could assist the investigation please contact police via the non-emergency number 101.

"Alternatively, you can call Crimestoppers in confidence on 0800 555 111."

There has been speculation that convicted murderer Peter Tobin is Bible John after Scottish criminologist Professor David Wilson popularised the theory.

Due to the deterioration of DNA samples, police were unable to confirm the theory.