A number of male suspects in the case of serial killer "Bible John" has given DNA samples.
The samples have come from men in their 50s and 60s
Detectives have renewed their bid to catch the killer, thought to be responsible for the deaths of three women in Glasgow in the late 1960s.
A spokeswoman for Strathclyde Police said: "We can confirm the investigation
is still ongoing."
The first victim Pat Docker died in February 1968, followed by Jemima McDonald and Helen Puttock.
The police spokeswoman declined to comment on the potential new breakthrough but sources close to the investigation said several men had been asked to provide the blood samples as part of the probe into the murders in 1968 and 1969.
Although hundreds of suspects were interviewed by police at the time of the deaths, only a few dozen are thought to have been asked to give DNA tests.
The men who have been targeted are now in their late 50s or early 60s.
Bible John is believed to have stalked Glasgow's dance halls 35 years ago.
The notorious killer met his victims at the Barrowland Ballroom, where he
charmed them and often quoted passages from the Bible.
Ms Docker, 25, was the first to die, followed by Ms McDonald, 32, 18 months later, and Ms Puttock, 29, 10 weeks after that.
Bible John frequented the Barrowland Ballroom
Some detectives at the time believed one killer was responsible for all three deaths but other colleagues were not convinced.
It is one of Britain's most baffling murder mysteries but police in Glasgow
have never given up in the hunt for Bible John.
The Bible John case returned in dramatic style to the public eye in 1996, when police exhumed for DNA tests the body of a man buried in a graveyard in Stonehouse, Lanarkshire.
They said later there was insufficient evidence from the tests to link him
with the scene where Helen Puttock was murdered.