Jurors have been urged to convict three people of the "horrific and brutal" murder of a schoolgirl.

Prosecutor Alex Prentice KC made his closing speech in the trial at the High Court in Glasgow on Monday.

Robert O'Brien, 45, Andrew Kelly and Donna Marie Brand, both 44, are accused of killing Caroline Glachan, 14, at the River Leven in West Dunbartonshire on August 25 1996.

The trio deny the accusation and have each lodged a special defence of alibi.

The trial has earlier heard how O'Brien had been in a relationship with Caroline at the time. He was around four years older.

The teenager was said to have left her best friend that night to go and see O'Brien, who was known as Robbie.

Mr Prentice stated to jurors: "Caroline Glachan was an excited 14 year-old girl wanting to meet 18 year-old Robbie O'Brien on the Black Bridge at the River Leven.

"She was looking forward to meeting him.

"What she was looking forward to turned out to be a horrific and brutal attack and (she was) left to drown in the River Leven."

The prosecutor said the evidence in the two week trial - both direct and in-direct - presented a "compelling and convincing case" against the trio.

Mr Prentice said: "The Crown case is that Robert O'Brien attacked Caroline with a blunt instrument and inflicted the 10 or so blows causing her to fall in the water and to drown.

"He is guilty of murder, nothing less."

He said Kelly and Brand - who O'Brien was also seeing at the time - are responsible on an "art and part" basis - a legal term of acting in "concert".

The advocate depute further stated: "I do not suggest that they plotted to murder Caroline Glachan.

"But, I do suggest that there was a plot to do harm to her.

"I suggest that what was intended was a confrontation of some kind which involved violence."

Mr Prentice said the evidence of Archie Wilson - then aged four and half in 1996 - was "pivotal" to the Crown case.

He did not testify personally during the trial.

But, his mother Elizabeth Wilson - known as Betty - did give evidence and recalled her boy claiming how he had been taken down to the river that night, saw a "lassie" get "battered" and fall into the water.

Miss Wilson had arranged for Kelly and his then girlfriend Sarah Jane O'Neill to babysit her children that evening.

O'Brien and Brand are also said to have ended up there.

O'Brien, Kelly and Brand deny going down to river and claim not to have left the property that night.

Mr Prentice said Archie had given an account of what he had witnessed before a body was discovered.

The prosecutor said: "I suggest that is highly significant. How would a wee boy know someone had been battered and fallen into the River Leven?"

The advocate depute further added Archie had been "recounting a lived experience".

Jurors went on to hear from O'Brien's lawyer Ian Duguid KC.

He claimed there was now a trial 27 years after the murder because some "people in the community" where the death occurred had "decided to change their evidence" from the time.

Mr Duguid suggested the jury is being asked to "close the book" on the case after all these years and convict someone of Caroline's murder.

The trial, before judge Lord Braid, continues.