Three people have been found guilty of murdering a teenager whose body was found in a river 27 years ago.

At the High Court in Glasgow on Thursday, a jury convicted Robert O’Brien, 45, Donna Marie Brand, 44, and Andrew Kelly, also 44, of killing 14-year-old Caroline Glachan in 1996.

During the 10 days of evidence, the jury heard Miss Glachan’s boyfriend O’Brien, plus Brand and Kelly had arranged to meet her on August 25 that year at a bridge near the towpath beside the River Leven, between Renton and Bonhill in West Dunbartonshire.

The trio shouted and swore at Miss Glachan and repeatedly punched and kicked her to the head and body.

The court also heard they threw bricks and other similar items at her, causing blunt force trauma to her head and body.

She was pushed or fell into undergrowth and her body was later discovered in the river at Place of Bonhill, Renton.

The jury retired to being deliberations on Tuesday and returned unanimous guilty verdicts for all three on Thursday afternoon.

During the trial, the court heard from Miss Glachan’s mother Margaret McKeich, who said her daughter was “infatuated” with her boyfriend O’Brien, who then went on to murder her.

Mrs McKeich said her daughter had previously disclosed O’Brien had “lifted his hands to her”.

Mrs McKeich said she did not approve of her daughter’s relationship with O’Brien, known as Robbie, as he was a few years older than her.

Her daughter’s body was discovered on the day of Mrs McKeich’s 40th birthday.

Upon returning from celebrations in the early hours of the morning, Mrs McKeich realised her daughter was not at home.

She received the news that her body had been found the following day, on August 25.

Later in the trial, Miss Glachan’s childhood friend Joanne Menzies, 42, told the court O’Brien had threatened to kill Miss Glachan for “kissing another boy”, and that she had seen O’Brien bully the schoolgirl on more than one occasion.

Dr Marjorie Turner, a forensic pathologist, told the court Miss Glachan’s ultimate cause of death was drowning.

She told the trial: “She was still alive when she went into the water. The drowning was the ultimate cause of death.”

Charges of assault against O’Brien were dropped during the trial.

Jurors also heard Brand “threatened to batter” Miss Glachan after she found out O’Brien was seeing both of them at the same time and Brand was “unhappy”.

The court heard three people said George Graham, who is now dead, confessed to being responsible for the 14-year-old’s murder.

Witnesses including his then girlfriend Jean McIntyre, who is now dead; his cousin, Margaret Connolly, who was 16 at the time, and Mary Rose Connolly, who is also now dead, gave statements to the police, telling them Graham had confessed to murdering Miss Glachan.