The mother of a 12-year-old boy stabbed to death 34 years ago today made an emotional appeal for new information about his murder.

Schoolboy Keith Lyon was found near his Brighton home 34 years ago this Sunday.

A day hasn't gone by in all those years when Valda Lyon, now 83, hasn't asked the questions why and who?

She speaks to a photograph of her then 12-year-old son Keith at her home every day and will be telling him of this article tonight.

Tears welled in her eyes as she spoke publicly in depth for the first time of how Keith's death had ruined her life, the life of her late husband, band leader Ken Lyon, and her 40-year-old musician son Peter.

Mrs Lyon joined a police press conference at Brighton police station where detectives vowed not to rest until the killers of a talented musician, a "nice boy who would stand up against injustice", had been traced.

It was May 6, 1967, when Keith left the family home in Ovingdean, Brighton, to buy a geometry set to use at school the following week.

He was walking across the Downs to shops at Woodingdean when he was attacked and stabbed 11 times in the chest, back and abdomen. No one knows why.

Boys were seen "larking around" where Keith's body was found. Another witness saw two youths running from the scene towards Woodingdean school and getting on a bus in Whitehawk Road.

The blood-stained murder knife was found by a wall and close by in toilets was evidence of someone having washed blood from their hands and clothes.

One theory is that he was picked on by young yobs because of the way he was dressed. Keith was smart, a Brighton and Hove Grammar School boy, and was wearing part of his uniform.

A massive police inquiry, during which 80,000 home visits were made and the fingerprints of 6,000 local schoolboys taken, produced suspects but no concrete evidence.

But detectives hope by relaunching their hunt for the murderer they will "prick the conscience" of anyone with information.

Detective Superintendent Dave Gaylor, heading the inquiry, said people had called in with names, but he said police needed more: "Why do they suspect these people? Did they witness something. Have they evidence?

"It is certain youths in the area were responsible or may have seen what happened. They are probably in their forties or early fifties now and may have had this on their consciences all these years.

"We want them to come forward now and talk to us."

And he pledged that the case would remain open until it has been resolved.

Mrs Lyon, who now lives in Hove, said her son's name will be on her last breath. She will never give up wanting justice for as long as she lives: "Every single day I think something will happen, but it doesn't. I think about him every day."

Reporters and camermen went silent as she told in detail for the first time of that sunny, blue-sky day in May.

"It was a Saturday and there was no school. We had been planning a family holiday and I went into Brighton to look for clothes."

The boy's mjusician father was playing at the Metropole Hotel on Brighton seafront when officers arrived to break the news. He went home and told his wife.

Mrs Lyon and Peter had been watching the film Twenty Thousand Leagues Under the Sea and she remembered saying 'It's a pity Keith isn't here. He would love this."

Children were kicking a ball, shouting, outside and Mrs Lyon thought Keith was among them when her husband arrived and told her.

She put Peter on her back and carried him upstairs to bed. Peter asked "why is daddy crying" and she told him Keith had been hurt and she would explain the next day.

Mrs Lyon: "I thought at that moment that was the end of the world.

"At least someone could let us know why it happened. There was no reason in the world why he should be murdered. He was just walking to the shops. It just hurts so much not to know. It has ruined our lives."

Retired Detective Superintendent Jim Marshall, who solved a record 100 murders in his career, could not bring Keith's killers to justice, but he is still trying.

He joined the press conference and admitted: "I get very sad. This has lived with me and rankled me from that day to this but I am still hoping it will be solved.

"People still stop me in the street and ask me about the case.

"I would plead to people in the strongest possible way to come forward and help the police."

Det Supt Dave Gaylor, leading the new appeal, said: "We still think the answers lie in the community of Brighton and that someone local knows what happened."

A Crimewatch appeal last year prompted some new leads but did not draw the police any closer to the killer.