Police are continuing to hold a man in connection with the hunt for the Yorkshire Ripper hoaxer Wearside Jack.
Johh Humble has spent two nights in police custody
Forensic teams have been examining the home of John Humble, 49, who has been arrested on suspicion of perverting the course of justice.
He is being quizzed by detectives investigating hoax letters and a tape which fooled police into believing the serial killer was from the North East.
Officers searched a house in Flodden Road, in Ford, Sunderland on Wednesday.
It is thought the arrest on Tuesday came after police recovered the hoax letters that were believed to have been lost and unearthed new DNA evidence.
The hoax letters and tapes, sent 27 years ago by a man with a strong Sunderland accent who claimed to have carried out the Ripper murders, taunted officers and diverted police attention away from West Yorkshire, as Peter Sutcliffe killed three more women.
Police have searched a house in Flodden Road, Sunderland
West Yorkshire Police have refused to confirm that the arrest was triggered after a "cold case" review by the force's new Homicide and Major Inquiry Team.
The squad is known to have been using state-of-the-art DNA techniques to check for breakthroughs in cases.
It is understood that envelopes from the letters may still exist - raising the possibility they could provide a DNA profile of the hoaxer through saliva traces.
Mr Humble is understood to be separated from his wife and now lives with his brother, named locally as Henry.
Yorkshire Ripper Peter Sutcliffe, from Bradford, now 59, was jailed for life in 1981 for the murder of 13 women.
In the late 1970s and 1980 his murders brought terror across the north of England and there was huge pressure on the West Yorkshire Police murder team, headed by Assistant Chief Constable George Oldfield.
But the inquiry was thrown off course after the three letters and a tape were sent to the investigation team by a man who was to be nicknamed Wearside Jack due to his strong Sunderland accent.