Donna Marie Brand, 44, was also found guilty of the murder but was said to be too ill to appear in the dock and is due to be sentenced in March.

O’Brien and Kelly have now made appeals for freedom after instructing their legal teams to challenge their convictions and the length of their prison sentences.

The three had denied murder but were convicted after a two-week trial after which Lord Braid described the killing as “brutal, depraved and above all wicked”.

The trial heard Caroline had been “infatuated” with O’Brien and had gone to meet him by the River Leven near the Black Bridge between Renton and Bonhill, where she lived, when the trio attacked her and left her to drown.

The killers – all teenagers at the time – repeatedly punched and kicked the schoolgirl and threw bricks at her, causing blunt force trauma to her head and body.

She was subsequently pushed or fell into undergrowth and her body was later discovered in the fast-flowing river.

The three were arrested after a cold case investigation was reopened in 2019.

Sentencing O’Brien and Kelly, Lord Braid said: “Caroline was a lover of life but due to both of you, Caroline has been deprived of the opportunity of living that life, becoming an adult, having children, fulfilling the potential she had.

“You have taken a daughter from a loving mother. She has been deprived of seeing the woman that Caroline would have become.”

Caroline’s mother, Margaret McKeich, leaving the High Court in Glasgow when she said  ‘justice has been done’ after her killers were jailed for life.

He told O’Brien he was the “principal perpetrator” and said no one could “fail to have been sickened” by the description of the injuries he inflicted on his victim.

The judge added: “One can only imagine the terror she must have experienced when she realised that this was to be no romantic encounter.

“It can be difficult to find words to describe the evil nature of your crime – but three that come to mind are brutal, depraved and, above all, wicked.”

Jurors previously heard how O’Brien had first met Caroline two months before her death and that her mother had challenged him about going out with a person much younger than himself.