By Julie Beanland
Producer, Real Story: The Ripper Hoaxer
Made with the full support of the police, a BBC ONE programme reveals how a cutting edge investigation finally solved a 25-year-old mystery, which had allowed the infamous Yorkshire Ripper to kill and maim with impunity.
Police studied the bogus tapes
The Real Story team was granted exclusive access to police interview tapes with John Humble, the petty thief who last week was sentenced to eight years in prison for being the hoaxer.
In the tapes Humble explains how he took his idea from the Jack the Ripper hoax letters of the 1880s.
The film also features the first ever broadcast of a phone call made by Humble to police in which he tried to call off the hoax.
At that time, one woman had been murdered while police focused on the search for him in Sunderland.
Barbara Leach was attacked as she walked home from a night out in Bradford in September 1979.
Her mother Beryl tells the programme that Humble's actions were "evil".
Beryl Leach's daughter was murdered during the hunt for a 'Geordie' killer
"Some may not have died if Humble hadn't hoaxed the police," she says.
"It's possible Sutcliffe would have been caught sooner."
Two other murders followed before the real Yorkshire Ripper, Peter Sutcliffe, was caught.
Using news archive material, the film tells the story of how, in 1978, police hunting Britain's most notorious serial killer received a letter from a man who claimed responsibility for the three-year reign of terror.
Another letter soon followed and then the biggest breakthrough of all: A taped message from the killer himself, taunting detectives about their inability to catch the man who had been terrorising the streets of northern England for the past four years.
Calling himself Jack the Ripper, he appeared to have inside knowledge of how and where the killer plied his deadly trade.
Desperate and exhausted, detectives leading the Ripper hunt were convinced it was genuine.
The hunt for the killer swung dramatically from Yorkshire to the North-East, because of the man's "Geordie" accent and the postmark on the envelopes.
In the weeks that followed, a £1m advertising campaign was launched, urging people who recognised the voice of the "killer" to come forward.
At the same time, police officers on the killer's trail were told they could eliminate any suspects who didn't have a Geordie accent.
The real Yorkshire Ripper Peter Sutcliffe was jailed in 1981
Tragically, that included Peter Sutcliffe - the Yorkshireman who would confess to the Ripper crimes three years later - but only after he had been interviewed at least nine times and eliminated because he had the "wrong" accent and handwriting.
In the intervening three years, Sutcliffe had murdered at least three more women and left four more for dead.
For the next 25 years, it remained an unsolved - and apparently unsolvable - puzzle, despite constant rumours that the hoaxer was a former police officer with a grudge.
But when West Yorkshire's newly formed Homicide and Major Enquiry Team - HMET - was formed early in 2005, they decided to open the file once more on the hoaxer.
They managed to recover fragments of the original letters and envelopes and subjected them to a barrage of sophisticated tests, using the latest DNA techniques.
The new tests eventually provided an amazing new breakthrough - a DNA profile.
And when that DNA was checked against existing criminal records, they found it matched a petty criminal from Sunderland, called John Humble.
Real Story: The Ripper Hoaxer highlights how much policing methods have changed since the 1970s.
These days, the primary tools of the detective are DNA, CCTV, telephone tracking and computers.
Back then, they were trying to catch a serial killer who picked his victims absolutely at random, without any of these.
Real Story: The Ripper Hoaxer follows the full story - from scientific breakthrough to the courtroom verdict. It goes out on BBC ONE on Monday 27 March, 2006 at 2235 BST.