Crimestoppers, an independent charity, has put forward a reward of up to £20,000 for relevant information supplied anonymously.

Detective Inspector McCrissican, from the PSNI's Legacy Investigation Branch, said: "We hope this reward will encourage those with information to tell Crimestoppers what they know and that information will, in turn, help us identify those responsible."

Marian, who was 18, was discovered at the bottom of a quarry near Aughnacloy on Saturday, 31 March 1973. She had attended a charity dance at Hadden's Garage in Aughnacloy on Friday, 30 March 1973, to hear her brother's band, and was last seen shortly after 1am leaving the event with a young man and walking towards Hadden's Quarry. Her body was found in the quarry at around 6am the following morning.

Detective Inspector McCrissican, said: "We believe Marian left the dance at Hadden's Garage with a man, walking in the direction of the nearby car park at the top of Hadden's Quarry about 400 yards away from the garage. We do not know what happened next, but Marian's body was found at the bottom of the quarry below the car park. "I appreciate this murder took place over 50 years ago but we would like to talk to anyone who was at the dance at Hadden's Garage on the night of Friday, 30th March, 1973. Marian went there with a girl friend to listen to her brother's band.  Did you see who she was dancing with or speaking with? Did you see her leave the dance with a man? Do you know who he was? Did you see her in the car park at the quarry any time after 1.15am on the Saturday morning?

"Additionally, do you remember anyone who was at the dance returning home distressed or with dirt on their clothes? Has anyone ever talked about the events of that night?

"Marian's family deserves to know what happened to her that night and our investigation continues.

"I am appealing to anyone who may be able to help bring some closure to the Beattie family to come forward and speak to detectives in Legacy Investigation Branch. Detectives can be contacted by calling 101. Alternatively, a report can be made online at reporting.psni.police.uk/appeals. Information can also be provided to police through the Major Incident Public Portal at: mipp.police.uk/operation/PSNI23S01-PO1. 

Alternatively, if you wish to stay anonymous or wish to be eligible for a reward, please contact the independent charity Crimestoppers anonymously on 0800 555 111 or online at www.crimestoppers-uk.org."

When contacting Crimestoppers, there is no caller line display, no 1471 facility and computer IP addresses are never traced.