Previously Donald Findley K.S. spoke in Stewart’s defense. He told the court that Stewart and Kayden Moy were once “close friends”.
He added: “But two groups were formed and began to behave in the same way. Violence was common.”
He said Stewart regretted what happened and was “very shocked” after his conviction.
Stewart was at the time subject to a pay order for possession of a machete, which had been imposed four days before the murder.
His other previous conviction was for breach of the peace with a knife.
Mark Stewart CC, representing Turley, said the 18-year-old “did not intend or want to kill Kayden Moy, but he accepts that he did it.”
Ian Duguid, in charge of the third teenager, said he was 14 at the time of the murder and his “immaturity” was highlighted in criminal justice social work reports.
He said the teenager had a “traumatic upbringing” and had since been working on educational projects from a safe place.
He will be held in a secure facility and then transferred to prison when he becomes an adult.
Moira Orr, director of homicide at the Crown Prosecution Service, said: “The three accused, all teenagers, became potential killers the moment they armed themselves with even one knife.
“And they became murderers. One of them, Cole Turley, struck the fatal blow, but prosecutors proved that all three participated in the planning and execution of the crime.
“It is difficult to adequately express the devastation caused by their decision to carry bladed weapons.”