On a Saturday night in a busy Edinburgh pub, Christine Eadie and Helen Scott were enjoying drinks with friends.

The 17-year-olds would meet up at each other's houses, listening to music and talking about make-up. Christine loved The Osmonds while Helen was a fan of David Cassidy.

They were just stepping out into the world and doing what countless young girls did, and continue to do, by arranging a night out in the city centre.

Ms Eadie had a troubled childhood and lived with her grandmother before moving into a bedsit in Leith. Described as outgoing and worldly-wise, she had a job as a shorthand typist in a surveyor's office.

She had known Ms Scott since she started Firrhill High School.

A family girl originally from Coldstream in the Borders, Ms Scott was very close to her mother, father and brother, Kevin. She still lived with them in the family home in Comiston, Edinburgh.

She had left school and had a job at a tartan shop, but was shy and not very streetwise. "She was outgoing," half-sister Diana Douglas said, "But she wasn't going to pubs and clubs and going out every weekend. She was nothing like that."

Agnes Brattisani, Ms Scott's other half sister said she had just started her first job and was a regular babysitter for her niece and nephew. She said Ms Scott had only had one boyfriend, from the Borders. She was, two sets of juries were to hear in more detail than any teenager would want known, still a virgin.

The two girls had met up on October 15, 1977, visiting various pubs before arriving at the World's End.

It was just before 10pm and it was standing-room only as the pair ordered drinks at the bar for them and their two friends.

One of the girls they were with spotted someone she knew and the group were invited to a party. Ms Scott and Ms Eadie turned down the invitation. As their two friends left, one of them said she always remembered Ms Scott, who said she wanted to go home, giving her a big smile. But the girls had met two men in the pub and started chatting to them.

They were Angus Sinclair and his brother-in-law Gordon Hamilton. The conversation did not last long, no longer than 25 minutes, and the pair were seen outside at closing time on the street soon afterwards.

A police constable was on duty patrolling his patch on the Royal Mile as usual and went to help Ms Eadie to her feet when he spotted her stumbling.

Ms Scott soon came forward to help her friend and Sinclair was standing nearby watching. He offered them a lift and the girls debated whether or not they were going to accept.

But he told them he would "take them where they needed to go" and they walked off in the same direction, the court heard.

Only one person alive knows what happened next and that is what detectives have spent almost 40 years trying to find out.

The beginning of what was then one of Scotland's biggest murder investigations began when Ms Eadie's body was found the following afternoon at Gosford Bay in Aberlady, East Lothian, while Ms Scott's remains were discovered a few hours later in a field near Haddington. The girls had been beaten, raped and strangled with their own underwear.

Ms Eadie's hands were tied behind her back with part of a pair of tights and her mouth had been stuffed with a pair of pants held in place by a bra.

The other leg of the tights was tied around her neck. Unlike Ms Eadie, Ms Scott was still wearing her top and her new coat, bought just days before. A charity sticker she had bought was still attached to her shirt. Her belt had been used to tie her hands behind her back. The belt from her friend's jumpsuit was around her neck. A footprint marked her face.

An extensive search was undertaken for missing items belonging to both girls. Ms Eadie's jumpsuit, black stiletto ankle boots, a blue coat with fur collar, a gold neck chain and a leather handbag which had a lighter with the word "Donny" painted on it were never found. Neither were Ms Scott's faded blue jeans, black clogs or black handbag.

Ms Scott's father Morain Scott, 84, said her mother Margaret was never the same again after that find.

The murder marked the start of his wife's ill health and she died in 1989 having never seen her daughter's killers punished.

But Mr Scott was in court to finally see justice for his daughter.