Aaron Campbell, 16, was today sentenced to at least 27 years in jail for his actions, which shocked the island community and Scotland.
Despite repeatedly denying any involvement in the crime during his trial, the teenager later told a psychologist that he had snatched the six-year-old from her bedroom on 2 July last year.
In his report, the psychologist said Campbell had described the moment he saw Alesha as a “moment of opportunity”, adding: “All I thought about was killing her.”
At his trial the teenager lodged a special defence accusing the partner of Alesha’s father of carrying out the crime, but the jury found him guilty last month in a unanimous verdict.
During the nine-day trial, the High Court in Glasgow heard that the schoolgirl had suffered 117 injuries and died from significant pressure applied to her face and neck.
At his sentencing hearing, Judge Lord Matthews said social work and psychologist reports “had painted a clear picture of a cold, callous, calculating, remorseless and dangerous individual”.
Describing what happened on the night of the murder, he said Campbell had been at a party drinking and later entered the house where Alesha was staying with her father and grandparents.
He was hoping to find some cannabis, having previously bought the drug from the six-year-old’s father Robert MacPhail, but instead found her asleep in her bedroom.
Lord Matthews also referred to a report prepared by forensic clinical psychologist Dr Gary Macpherson, who interviewed Campbell about his crimes after his trial.
He said: “When you saw Alesha your reaction, according to you, was as follows: ‘A moment of opportunity...At any other time in life, murder wouldn’t have been the conclusion.
“‘If I was a year younger I don’t think I would have done it…All I thought about was killing her once I saw her’.
“You said that Alesha was drowsy and became a bit more awake when you went out. At one point she asked who you were and where you were going. You said you were a friend of her father and that you were taking her home.”
The judge said he had taken her to a secluded spot where he “violated and murdered her in the most brutal fashion”, later saying he was “quite satisfied by the murder”.
Campbell also told Dr Macpherson that at points during his trial, where the severity of the crimes were extensively detailed, it took “everything to stop laughing”.
Sentencing him to life in prison with a term of 27 years before he can apply for parole, Lord Matthews said the boy’s reintegration into society might prove to be “impossible”.