The trial heard that the trio went on to create a rap song mocking Moy and Turley had acted out the murder on the couch of a friend whose flat was used as a hide-out.

Turley pleaded guilty. Stewart and the 15-year-old both denied murder but were convicted in June after a trial at the High Court in Glasgow.

Meanwhile, last week Stewart posted a video online from jail in which he appears to boast about stabbing Kayden.

The video, filmed in a cell in HMP Polmont and posted on Snapchat, shows Stewart topless, masked and rapping about the killing – claiming he will act violently again once he is released.

The BBC understands the Scottish Prison Service has taken action following an investigation into the incident.

A spokesperson said: “While we do not comment on individuals, we continue to work with Police Scotland, and other partners, to take action against those who breach our security.

“We understand the lasting impact this kind of offending has on families as well as the significant distress such videos can cause.

“Our staff work hard to keep prisons safe and secure, using all available technology and intelligence to prevent illicit items, including mobile phones, entering our establishments.”