Muriel Drinkwater was 12 when she was raped and killed.
Scientists working on the case of a schoolgirl raped and shot dead 62 years ago have made a possible breakthrough in the hunt for the killer.
Muriel Drinkwater, 12, was attacked as she walked home from a school in Penllergaer, Swansea in June 1946.
Forensic experts have now obtained a DNA profile related to the killer's family from a semen stain on her coat.
It means police could trace her killer even if he is dead by matching his profile to a close male relative.
Dr Colin Dark, from the Forensic Science Service, said it was the oldest case in the world that he was aware of that a DNA profile and familial profile had been obtained from.
Attempts to match a DNA profile of the suspected killer have so far failed, because his details are not on the national DNA database.
How the DNA profile could help detectives.
Det Ch Insp Paul Bethell from South Wales Police, who is conducting the new investigation, said Muriel's killer was probably aged 18 to 25 when he murdered her, so would now be aged at least 80, if alive.
He said he was focusing on 40 to 50 men who featured in the original investigation.
If any of the men emerged as strong suspects, DNA would be taken from them or, if the men were dead, from their male relatives, to establish if there is a link to the crime.
None of the suspects or their relatives had been swabbed so far.
Scientists used a technique called Y-STR to gain a familial DNA profile from the stain, which enables them to examine specific DNA markers on the Y-chromosome, which is passed from father to son relatively unchanged throughout the generations
Familial searching was crucial to police solving the 1988 murder of 20-year-old Lynette White in Cardiff.
A search of the national DNA database for a rare gene variant found in a specimen recovered from the crime scene identified a 14-year-old boy with a similar genetic profile.
This led police to his paternal uncle, Jeffrey Gafoor, the murderer. Gafoor received a life sentence in 2003 for the killing.
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