IT has taken former police sergeant David Blackie two-and-a-half years to write his book on the shooting of planning officer Harry Collinson.

Yet, throughout his interviews with people most affected by the chilling murder, there has always been a common theme: "It should never have happened."

"That is the one line which comes up time and time again," said Mr Blackie, of Barnard Castle, County Durham.

"What I've tried to do is provide an even-handed account of how it happened."

Mr Blackie, 48, was one of four firearms instructors and tactical advisors at Durham Constabulary, who was sent to Butsfield, near Consett, after the shooting on June 20, 1991.

Ironically, the victim was the son of his next-door neighbour, Mabel Collinson.

The murder of the Derwentside District Council official had a profound effect on Mr Blackie, and, not surprisingly, research for his book proved a cathartic experience.

"The shooting incident did have a tremendous effect on me, not only because he was Mabel Collinson's son, and so I knew him to speak of, but also because there were implications of what I felt about the police during the whole situation, and what they had and hadn't done," he said.

The sergeant resigned from the force in 1992 and went on to run the restaurant, Hogarth's, in Darlington.

During research for his book, he spoke to Dryden's sister Elsie, Harry's brother Roy, and, of course, Dryden himself, who had not previously given interviews since his conviction.

The killer was a difficult interviewee and refused to show remorse for his actions, said Mr Blackie.

"You talk to him and you sense that he feels totally justified for what he has done," recalled Mr Blackie.

"I did lose a lot of sympathy for him. The people I did feel sorry for were his family. It was very difficult for them. They were tremendously supportive of him but even they had a lot of regard for the Collinsons."

A number of police officers declined to talk to Mr Blackie, but others were more forthcoming and have given a remarkable insight into events leading up to the shooting.

"I think I was able to convince them that I didn't want to do a hatchet job on anyone, the council or the police, it was just a factual story which really needed telling."

The account, which has been called Manstopper after the gun Dryden used to shoot Mr Collinson, has been seen by a number of publishers who have offered positive comments but no deals yet. The author also believes it has potential for television and has sent a copy to North-East actor Tim Healy, who has shown an interest.

"I've written it for every sort of public body, the police, local authorities, whatever, to be aware that something which is potentially quite insignificant can blow up into something as tragic as this.

"I think that is basically what people should take away from it."