Arguably anyone who’s swept up by “extremist” ideology and prepared to kill people for their cause and possibly kill themselves in the process, has a mental illness.
Though most of us have some form of mental illness throughout life or know someone who has. Not that we necessarily want to go out killing people usually.
Anyway, once again it’s dropped to the bottom of the news the instant they’ve decided it’s not terrorism. That’s okay then, just some “crazy nutter”* 🙄
(* and I’m being sarcastic in that. I mean that’s how the news channels and papers will see him, rather than someone who needed help).