If ever a stretch of Sussex downland was inappropriately named, it was Happy Valley near the Brighton estate of Woodingdean.

For it was there in May 1967 that 12-year-old schoolboy Keith Lyon was stabbed to death on a bridle path.

It happened more than half a century ago yet the killer has never been brought to justice. The murder was one of the few unsolved by Detective Chief Superintendent Jim Marshall, soon to be head of Sussex CID.

Keith, the son of Brighton bandleader Ken Lyon, lived in a historic house at Ovingdean. He decided to go for a walk before music practice.

He went on to the Downs clutching two shillings which his father had given him as pocket money. Keith had intended to buy a compass for his geometry set.

About 15 minutes after he had set out, Keith was in Happy Valley nearing Warren Road when he was stabbed 11 times. His body was left near the side of the path and was discovered shortly afterwards by a teenage girl.

Keith, who attended Brighton, Hove and Sussex Grammar School, was wearing a white shirt, blue sweater, school tie and grey trousers. He might have been attacked because he looked smart.

The area was cordoned off by police and a huge investigation began with Scotland Yard joining local detectives.

Boys who went to the nearby Fitzherbert School in Woodingdean found a steak knife on the ground and this was probably the murder weapon.

Detectives deduced that the murderer had probably climbed over a flint wall into the school grounds after committing the crime.

There were reports of scuffles between boys at the place where the body was found and bloodstains were discovered at the toilets in Lawn Memorial Park.

Hundreds of people were interviewed about the crime. They even included girls at Roedean School about a mile away.

Later 4,500 boys were fingerprinted and huge numbers of house calls were made. A mine-detecting vehicle was brought in to see if any other weapons were there.

A year after Keith’s death, Ken Lyon offered a reward of £1,000 for information leading to the killer’s arrest and conviction.

But no one was ever found and at Keith’s inquest the verdict was murder by a person or persons unknown.

Talking to police years later about the case, I was told they did not have enough evidence to bring a prosecution.

I also interviewed Ken Lyon who by this time had moved to a flat on Hove seafront. He had been broken by the crime and died in 1991.

Keith’s brother Peter continued to take a keen interest in the case and ten years ago police arrested two middle aged men. But they were never charged and were later released.

The murder of Keith Lyon shocked Brighton and Britain. It was a sad waste of a promising life and the vicious killing seemed to be completely random. It is chilling to think that the person or persons involved may still live in the area.