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.

On this occasion the school friends met up on October 15 1977, visiting various pubs in Edinburgh 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 bustling 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. Helen and Christine turned down the invitation, Helen saying she wanted to go home.

As their two friends left, one of them said she always remembered Helen giving her a big smile.

But the girls had met two men in the pub and started chatting to them.

The men 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 Christine to her feet when he spotted her stumbling.

Helen 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-ever murder investigations began when Christine's body was found the following afternoon at Gosford Bay in Aberlady, East Lothian, while Helen's body was discovered a few hours later in a wheat field near Haddington.

The girls had been beaten, raped and strangled with their own underwear.

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

The other leg of the tights was tied around her neck.

Unlike Christine, Helen was still wearing her top and her new coat, purchased 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. Christine'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 Helen's faded blue jeans, black clogs or black handbag.

The ligatures became crucial evidence. They were constantly reviewed as science moved forward through the decades.

It was the advent of DNA profiling that jump-started the case and eventually led police in 2005 to Sinclair and Hamilton, who was now dead.

Sinclair took to the dock in 2007 charged with the murders but the case collapsed mid-trial.

For the families of both girls, the past five weeks meant they were faced with reliving for the second time in court how they were told their daughters had been killed.

Helen's father Morain Scott, 84, said her mother Margaret was never the same again.

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

But Mr Scott was there to see Sinclair enter the witness box and hear his "ridiculous" version of events. He was there to finally see justice for his 17-year-old daughter when Sinclair was convicted of brutally murdering her and her friend.