Officers hunting the killer of Barbara Mayo, 24, who was raped and strangled in October 1970, will seek to obtain a DNA sample from a suspect.

Ms Mayo had been hitch-hiking from London to her home in North Yorkshire at the time of her death. Her body was found dumped near Junction 29 of the M1 in Derbyshire.

The largest murder investigation by any police force at the time failed to track down her killer.

Derbyshire police will go to court in Canada

But a breakthrough came in 1997 when new genetic finger printing techniques offered fresh hope.

A list of 250 men were identified as possible suspects and asked to give DNA samples.

One of the men on the list - who was living in the south of England at the time of the murder - has since moved to Canada.

He is understood to be an elderly man who is being treated for mental illness.

Detective Superintendent John Langley, who has been leading the hunt for the killer, said: "We are now left with just a handful of men who have either gone abroad or we are unable to trace."

He said officers had already got samples from men in New Zealand, Australia, the USA and Ireland.

"The man in Canada has a diagnosed medical condition and we need the permission of those treating him to take a DNA sample - to do this we are seeking the assistance of the Canadian authorities," said Det Supt Langley.

Officers have refused to give any further details about the man and stressed he was just one of a number of suspects.