The hunt for the man behind one of the most costly hoaxes in British criminal history, has been called off.
Peter Sutcliffe was arrested for a traffic offence
After 25 years, police say they could no longer prosecute the man - dubbed Wearside Jack - who sent letters and a tape to police claiming to be the Yorkshire Ripper.
Detectives believed the messages - which boasted about how police had failed to capture the serial killer - were genuine and diverted attention to Wearside, away from the real murderer, Bradford's Peter Sutcliffe.
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 in West Yorkshire were so convinced he was the murderer, that for a time they switched the hunt to the north-east of England and spent about £1m on a massive publicity campaign.
Officers even followed up on Wearside, while Sutcliffe went on to kill the last three of his 13 victims.
A spokesman for West Yorkshire Police said: "The offender can not now be prosecuted for the charge of wasting police time, because of the time that has expired.
"We have no plans to continue with the matter."
The spokesman also said that further forensic examination of the letters and audio tape could not be done using modern-day techniques because chemicals used in the 1970s would contaminate any new test.
The letters and the tape are to be kept under lock and key by West Yorkshire Police.
A spokeswoman for Northumbria Police said they accepted the decision of their West Yorkshire colleagues.
Less than 24 hours after the tape was made public, 700 people called hotlines in Halifax, Leeds and Sunderland, claiming to identify the voice.
Sutcliffe was eventually arrested and charged in South Yorkshire in 1981.
He was jailed for life in the same year, but later ruled to be criminally insane and was committed to Broadmoor