Profile: Troubled boy who admitted killing Bailey Gwynne
Killer described himself as 'fat' and told officers he carried weapons to 'be cool'.
The argument that led to Bailey Gwynne's death was so trivial it could have taken place at any school in any town anywhere in the world.
A seemingly innocuous exchange of words between teenage boys over a biscuit built up into a trade of insults and from there to an exchange of blows.
What made this everyday flare-up end in tragedy rather than bruised egos or a bloody lip was simply that Bailey's 16-year-old killer had a knife and in the heat of the moment he struck one fatal blow directly into his victim's heart.
The five-day trial heard the only chance Bailey would have had of surviving the 4cm wound would have been if the knife had been plunged into his chest right outside the doors of a hospital operating theatre, with surgeons on standby. Even then, the court was told, his odds of living would have been slim.
The fact his killer had delivered that one stab wound was accepted by both prosecution and defence.
The case hinged on whether or not he had intended to kill Bailey. An offer tabled before the trial, started by his defence team to plead guilty to the lesser charge of culpable homicide, was rejected by the Crown.
During the hearing at the packed High Court in Aberdeen a picture emerged of a troubled boy.
The court was told how the boy, who even now at the end of proceedings cannot be named because the law prohibits naming anyone under the age of 18 in criminal cases, had a turbulent family life and was the victim of bullying during his time at school.
He told police during an interview the day after the stabbing he had "never fitted in" and carried weapons in an attempt to "be cool".
When asked by police to describe himself, the child said he was "fat" and witnesses said he was often teased for his weight.
He told detectives how he bought the knife used to stab Bailey from the online retailer Amazon and had it delivered secretly to the house he shared with his mother.
The 16-year-old said he purchased the knife over the internet because "they don't check if you're over 18".
He also bought knuckledusters online and the internet history on his laptop showed Google searches including "illegal knives UK" and "knuckledusters UK".
The phrases "Aberdeen stabbings per 1000", "difference between homicide and murder", and "how to get rid of someone annoying" had also been searched.
A witness told the High Court in Aberdeen the killer was seen with a knife "maybe 25 times" before the fatal stabbing and the accused admitted that he regularly carried it with him.
He had recently started working at a fast food restaurant and was saving to buy a motorbike but told officers he had no hobbies other than "TV and computers". He said he sometimes drank alcohol, which he kept in his room, but that he had never used drugs.
When he was told by police the day after the killing that he was to be charged with the murder of Bailey Gwynne he broke down.
"But I tried to save him", he told officers.
He was then taken to Polmont young offenders' institution in Falkirk to be held until trial.
His defence team decided not to put the accused boy on the stand, instead inviting the jury to consider his reaction in the heat of a fight as a tragic mistake, but a mistake nonetheless.
In the end the jury agreed and took less than two hours to dismiss the murder charge and find the boy guilty of the lesser charge of culpable homicide. He is likely to return to Polmont after Monday's verdict.