I think he's a loner and an introvert who has been faking it for a very long time.
We know his birth registration is a forces one and his father was apparently in the army, and if we speculate about how that affected his early childhood, we might guess there were a lot of moves and changes of school etc. There's a heap of evidence that multiple moves in childhood correlate positively with mental health problems, suicide attempts, violent crime and a range of psychosocial problems. At a very basic level, kids who have to move and start again repeatedly can become transactional in their relationships in order to be accepted, which often means adopting a persona that's not authentic, e.g. cool kid, bad boy, class clown. As well as being unhealthy psychologically, that could account for why no one seems to know him very well - I think he's a chameleon who behaves differently with different people and now nobody quite recognises him in what they're hearing.
Inauthenticity is stressful, and I'd speculate that music has been an outlet for him - a thing he can do by himself and then parlay into a social activity. I imagine he's spent long hours in his room at home, practising guitar and writing songs. (I wouldn't mind betting there's some bad poetry yet to come out too.) I'm wondering whether the band starting to take off, and that very personal form of self-expression suddenly becoming public and being appropriated by others, has felt like a klieg light being shone on his private self. I can imagine that could have created an intolerable sense of pressure that might then have been released by an act of extreme violence.
I'm not making excuses for him btw, rather the reverse. I'm very interested to hear what comes out regarding his psychiatric state and I think it will be completely normal.
As ever, just my very subjective and speculative opinion.
Also important to remember at all times that none of the charges have been proven.
