Police are to examine a claim that the prime suspect in the search for the Yorkshire Ripper hoaxer known as "Wearside Jack" was a police officer.
Peter Sutcliffe killed 13 women before being caught
The man tricked police into believing he was the Yorkshire Ripper while the real killer murdered three more women.
A West Yorkshire detective, second in command in the Ripper inquiry, said an officer had been the main suspect.
West Yorkshire Police said they were examining the claim. The officer and the force he worked for were not named.
The hoax messages boasted about how police had failed to capture the serial killer, diverting attention away from the real murderer, Peter Sutcliffe, who is serving life for the murder of 13 women.
The hoaxer, who had an accent said to be from the Castletown area of Sunderland, sent police three letters and an audio tape at the height of the Yorkshire Ripper inquiry in 1978 and 1979.
Detectives were so convinced he was the murderer that for a time they switched the hunt to Sunderland.
During that period Sutcliffe, from Bradford, was questioned and eliminated. One of the reasons was that he did not have a Wearside accent.
Retired Det Supt Dick Holland, second in command of the ripper inquiry, told the BBC on Monday that a police officer serving at the time of the inquiry was suspected and the officer's old police notebooks were examined.
However, four or five of the alphabet characters did not match the hoax letters so he was never arrested.
Mr Holland did not identify the officer or the force he had served with.
He explained why the hoaxer was not hunted down by the Ripper inquiry team.
He said: "It was realised the letters and tapes were a hoax and misled us but we decided to put this to bed because the best thing to do was to get the force back on an even keel and get everybody working at the basic job of policing West Yorkshire and just learn by it."
But Patrick Lavelle, author of Shadow of the Ripper which examines the Wearside Jack story, said: "Even if there is the remotest possibility that he was a hoaxer, then there needs to be an inquiry.
"It didn't just cost millions of pounds of taxpayers' money, three women were killed while police were hunting a ripper from Wearside."