Imraan Ismail Vohra vanished as he walked home from school and his partially-clothed body was found two days later in Avenham Park, Preston, Lancashire, on July 13, 1985.
He had played a game of marbles with his friends at Frenchwood Junior School before setting off for his home in James Street.
Robert Morley, a petty criminal from London who was living in the Lancashire city at the time, has been identified as his killer thanks to the use of“familial DNA”. He died in Essex in 1997, aged 62.
Detective Chief Superintendent Graham Gardner, head of crime for Lancashire Police, told BBC Radio Lancashire: “We’ve known from 2002 we’ve had a part-profile of the killer from the scene.
“In six years we’ve tested 1,400 men against that sample. There’s been further advances, such as ‘familial DNA’, which allows us to arrive at an offender through family members.
“Morley doesn’t stand on the national database because he died but we were able to identify him through family members.”
Scientists say that, according to the DNA evidence, the chances of him not being responsible for Imraan’s murder are a billion to one.
Gardner said thatImraan’s family “have conducted themselves with great dignity in the most distressing circumstances for many years”.
He added: “There’s no happy ending to this story, but in some ways it does bring some conclusion to them. I would have liked to have seen this man brought to justice in Crown Court.”