'Helpful' details about Sean McGann's murder in Northampton more than 40 years ago have been given to police since re-appealing for information about the boy's shocking death.
The 15-year-old boy's body was found in an alleyway near Birchfield Road East, Abington, the morning after he was due to visit a funfair in April 1979.
Detective Chief Inspector Joe Banfield said: “Following our re-appeal on the 40th anniversary of Sean’s murder, we received some helpful calls and pieces of information from members of the public which we are continuing to work through.
“I would like to take this opportunity however, to appeal again for people to come forward if they know anything they think could be helpful to our investigation.
“I am convinced someone out there knows something and I would ask them to search their consciences for the sake of Sean’s family and tell us what they know."
Sean left his grandparents' home in Victoria Gardens sometime between 5.30pm and 6pm on April 17, 1979, to visit the funfair at Midsummer Meadow.
He was supposed to be home by 7pm but never showed up - his body was found in an alley near Birchfield Road East at around 8am the following morning.
Police believe the 'lovely' boy was strangled in a potentially sexually-motivated killing somewhere else but his body was in the alleyway for less than an hour.
His belt and shoes were found nearby but his glasses and jacket were never discovered, suggesting he could have been in a house overnight.
An anonymous letter, sent to the McGann family in 1991, that purports to have information that could lead to the killer was uncovered recently.
While graffiti saying 'very sorry' and 'no I'm not' close to where the boy's body was found was revealed in September 2019.
DCI Banfield added: “If you don’t want to come directly to us with your information, you can contact Crimestoppers anonymously on 0800 555111, but please come forward because Sean and his family greatly deserve justice."