A mother has said she is "running out of time to see justice done" for her son who was murdered 40 years ago.
Gary Miller and John Greenwood were beaten and hidden under a mattress in Whiston, Merseyside on 16 August 1980.
Making an appeal on Crimewatch Roadshow, Gary's mother Alma said they had been "just normal 11-year-old children... they did nobody any harm".
Merseyside Police have urged an unidentified "lone white" man seen near the site at the time to come forward.
Speaking to the BBC One programme, John's mother Barbara also said she needed to see her son's murderer caught.
"We feel like we've let the boys down [as] they've never had their justice," she said.
"[Their killer] deliberately left them to die. I can't that out of my head."
The school friends were found by a dog walker at the site of a disused colliery on Pottery Lane, which is now Stadt Moers Park, at about 19:20 BST. They later died in hospital.
A man was acquitted of murder in 1981, but new leads reopened the case in 2016.
However, it was dropped two years later due to insufficient evidence, a move which also saw the force apologise for failings in the original investigation.
Speaking as part of the new appeal, Det Ch Insp John Williams said the unidentified man, who was seen by the dog walker, was described as about 35 and white, with dark hair that was swept back. He was also said to be wearing a brown jacket.
"We would like to know, were you that person or do you know who that person was?" he said
"It would mean everything if I could give the two families some sort of closure."