"Weird and horrible" knife obsession of Bailey's killer

We've been hearing from a friend of the 16 year old boy who killed Bailey Gwynne at his school in Aberdeen. He's been sentenced to nine years in jail for culpable homicide, and carrying knives in school. The friend saw the fight which led to the fatal stabbing - and he's described the killer's fascination with knives. We've disguised his voice for legal reasons.