GERTRUDE Canning was just 20 when she was killed.

The young Wren, based in Scotland, went to post a letter to her family in County Donegal - but was never seen alive again.

No one was ever caught for the murder but, 71 years on, the death has inspired two new books. Both claim there was a "cover-up" - and one author says he will finally name the 'killer'.

Gertrude had lived in Milngavie, near Glasgow, before the Second World War broke out and when she became a Wren she was based at HMS Quebec, a Royal Navy base that was part of No 1 Combined Training Centre at Inveraray, in the then Argyllshire.

On June 30, 1942, she left to post that letter. After being reported missing, her body was found after a huge manhunt. She had been shot four times.

Five days after her death, a car-load of experienced Glasgow detectives, including Detective Inspector (later Detective Chief Superintendent) Robert Colquhoun arrived in Inveraray to investigate. But they were never able to find the killer.

Mr Colquhoun, who led the police investigation, wrote in his memoirs years later that it was his theory the killer "in all probability" died during the Allies' huge raid on the German-controlled French port of Dieppe in August that year.

Today, Glasgow author and journalist RJ Mitchell - readers of the Evening Times' sports pages will know him better as Bert Mitchell - believes there was a cover-up over Gertrude's death to avoid further damaging national morale after the failure of the Dieppe raid.

Mitchell was inspired by the case to write his latest book, The Longest Shadow, which is published this Thursday.

A nephew of Gertrude's, Liam Canning, is also working on a book about the case. It is believed his book will name the person he thinks killed her.

The Combined Training Centre was hectically busy during the war, training huge numbers of service personnel in the latest techniques of small landing-craft amphibious warfare.

Ex-DCS Colquhoun wrote in his 1962 memoirs, Life Begins At Midnight, that on the day Gertrude disappeared, she was seen by two road workers.

They spotted Gertrude, who was wearing her uniform, as she walked along a quiet wooded track, 100 yards from Loch Fyne's shores. A few minutes later, they saw a soldier walking down the track, in the same direction.

Forensic tests said three of the four bullets recovered from Gertrude's body could have proved fatal.

The weapon was a standard British Army .38 revolver. As Colquhoun wrote: "Several thousand men within a 10-mile area ... had this type of revolver and ammunition."

Test bullets from revolvers belonging to several thousand Commando troops were fired into cotton wool wadding and then analysed.

Troops who left the base were tracked down to mainland England and the Isle Of Wight. Battle-weary commandos who returned from action in Dieppe also had their bullets tested. But no match was ever found for the bullets that had ended Gertrude's life.

Mitchell, who was previously a Glasgow police officer for 12 years, is critical of some aspects of the original police investigation.

"The roadmen said they saw the soldier," he says. "It would not have been difficult to get descriptions and to get an artist's impression done and to compare this against all the soldiers' mugshots and to see which branch of the Armed Services he came from. Something does not seem right. I think there was a cover-up.

"The Allies' raid on Dieppe was a disaster and damaged morale. The war at that time was still in the balance as far the Allies were concerned. Suddenly, you have a girl being murdered by a soldier based at the CTC, which would have had a further impact on morale.

"You could perhaps understand the authorities' desire for the full story of Gertrude's murder not to come out. I am convinced the military and civilian authorities at the time would have been working in conjunction."

Mitchell says it is possible Gertrude was murdered by an officer. He says he learned from a military expert that the .38 revolver was issued only to NCOs and those officers who held the rank of Second Lieutenant or higher.

"It's possible," he says, "the killer was well-connected; if his identity had come out, it would have created a major scandal." He does, however, concede he has no proof of this.

Liam Canning, a nephew of Gertrude's, is writing a book about his aunt, which he hopes will be published next year. He has devoted the last decade to piecing together details of his aunt's life and death.

The family met senior officers from the then Strathclyde Police and were allowed to examine papers from the decades-old investigation.

Says Liam: "For obvious reasons I do not want to say too much about the book at the moment." The killer, if he is still alive, would now be aged about 90.

He adds: "It seems the murder of Gertrude was a crime that the authorities at the time, in light of the war situation, probably thought would have been bad for morale among the forces, especially as Britain's troops were preparing for the invasion of Europe."

Asked whether there could be legal ramifications about publicly naming the killer, he said: "It is possible, but I don't believe there will be.

Even if there were, I think all they would do would be to highlight what happened to Gertrude."

Police Scotland said: "This is very much an active inquiry and we would welcome any information from the public on the incident."

An Army spokeswoman said it did not have ready access to the records of personnel who trained at Inveraray or of those who were killed at Dieppe, and said it was unable to make any comment.

l The Longest Shadow, by RJ Mitchell, published by Fledgling Press, £9.99. He will be signing copies at WH Smith, Argyle Street, on November 23, 11am-1pm.