THE prime suspect for a hoax that allowed the Yorkshire Ripper to carry on killing was a policeman, the man behind the hunt for Peter Sutcliffe has revealed.

In 1978 and 1979, Wearside Jack, as he became known, sent police three letters and an audio tape claiming to be the serial killer.

Police were convinced he was the Ripper and switched their inquiries to the North-East for 18 months, during which time Peter Sutcliffe killed three more victims.

Dick Holland, who was second-in-command of the Ripper inquiry led by West Yorkshire Police's assistant chief constable, George Oldfield, said the former police officer, who was born and grew up in the North-East was "the best suspect we ever had".

And he revealed that the Deputy Chief Constable of West Yorkshire Police at the time, Austin Haywood, was "absolutely certain" the man was the author of the "I'm Jack" hoax letters and tape.

During the Ripper inquiry thousands of men in the North-East were interviewed, their handwriting was analysed and their voices compared with that on the tape.

They were also asked their blood type, as the letter writer was of the rare B secretor blood grouping.

Mr Holland said the former police officer was eliminated because he was not the serial killer and because three characters of the alphabet as written in his police notebooks or other documents did not match the those in the hoax letters.

He confirmed that every other character of the alphabet matched perfectly and no comparison was made between the man's voice and that on the tape.

He said: "As far as I am aware there were also no inquiries to determine the police officer's blood grouping.

"There was a suggestion in the inquiry that the author of the tape and letters could be a police officer with a grudge against George Oldfield.

"There was also the evidence of the two voice experts, who were certain that the man who made the tape was from a certain area of the North-East and we concentrated on that area.

"When police officers were suggested, we checked out all officers from that area and any officer who had any reason to commute between the North-East and West Yorkshire."

The handwriting of the 100 or so officers was examined and five or six were similar. "But there was one which was very similar," he said, "so we rushed it off for analysis."

He added: "On the matters that I dealt with, and I dealt with a hell of a lot, he was the best suspect for the hoax letters and tape.

"The deputy chief constable was absolutely certain he was the best suspect."