A POLICE investigation spanning three decades will come to an end today when the man behind the infamous Wearside Jack hoaxes is jailed.

John Humble will be sentenced at Leeds Crown Court for diverting the Yorkshire Ripper inquiry to the North-East and sparking a probe that cost £6m.

The 50-year-old yesterday admitted four charges of attempting to pervert the course of justice by sending a tape and three letters to detectives and a national newspaper between 1978 and 1979.

The real murderer, Peter Sutcliffe, was not arrested until January 1981, by which time three more women had been killed.

Humble confessed he started the hoax - probably the biggest hoax in the history of British criminal investigation - because he was bored.

When the jobless labourer was caught by police last October, he told detectives he knew what he had done was evil and that he regretted it.

At earlier court hearings, it was revealed that he accepted sending the hoaxes but would be pleading not guilty to the charges because he had not intended to trick the police.

Yesterday, it emerged he told detectives he wanted to help the investigation, although he did accept that what he had done was "evil".

But it was also revealed that, at the height of the publicity surrounding the letters and tape, Humble called an incident room that had been set up in Sunderland to tell police that they were a hoax.

A recording of the phone call he made was played in court, and Humble could be heard telling an officer: "Tell him it's a fake . . . the tape recording . . . the one he has just received."

Humble had sent the tape and two of the letters to Assistant Chief Constable George Oldfield, who by that time had spent four years hunting the Yorkshire Ripper.

Mr Oldfield took the decision to play the tape to a news conference in June 1979, and believed the sender to be the serial killer.

At his trial, Peter Sutcliffe said of the hoax: "I thought it was a diversion so I could be left to carry on. It served to take a great deal of the investigation elsewhere."

Paul Worsley, prosecuting, told the court yesterday that Humble had a fascination with the 19th Century murderer Jack the Ripper.

He said Humble would borrow books about the killings in London from his local library in Sunderland, and based parts of his letters on similar hoaxes sent to police at the time.

In one of his interviews with police, Humble claimed one of his reasons for writing the letters was "notoriety", and in another he said: "I was bored, I was on the dole and had nowt to do."

Humble was identified as a suspect when a cold case review was carried out by West Yorkshire Police last year, and DNA from one of the envelopes was matched with an entry on a national database.

The match was with a man from Sunderland who had been cautioned for being drunk and disorderly in 2001. Police arrested Humble at his home in the city's Flodden Road.

Last night, one of the language experts who was brought in to help the inquiry said he was astonished the hoaxer had been caught after all these years.

Retired phonetics lecturer Jack Windsor Lewis said: "I thought they would never find him or find him straight away. I am amazed it has come after all this time."

It also emerged yesterday that the huge police investigation on Wearside almost uncovered Humble more than 20 years ago, but he was never questioned.

He told police that his next-door neighbour was quizzed, and said: "I couldn't believe they never got me because they were checking everyone."

Mr Worsley said Humble's motive for the hoaxes was from a hatred of the police because he had been jailed in 1975 for kicking an off-duty officer in the head.

Humble's barrister, Simon Boure-Arton, is expected to make mitigating arguments this morning before the Recorder of Leeds, Judge Norman Jones, sentences him