That audition video is an eye-opener. He openly talks about flaws within his appearance... his fear of going bald. He talks about his 'obsession' with his looks and needing to look good. For me this is at the heart of this whole thing.
We live in a society today where appearance, fame and social media dominate life. LM was caught up in this - he was vain, he craved fame and used social media to try and promote a false celebrity. As he aged, did he become desperate? Did he start to take jobs - including making videos - to earn enough money to keep having surgery and maintain what he believed was so important - looks. He's talked about careers ending at 30 after all. He's 29.
And along the way maybe he lost the sense of reality and spiralled out of control, leading to the moment he killed another man and filmed the gruesome event. That audition video merely shows a polite, personable young man who is too concerned with his appearance. Somewhere along the way that person turned into a psychopath.