He may well be a Muslim convert, though that's only coming from unnamed sources as are the statements about "beheading". It wouldn't be the first time if the tabloids got that wrong (or made it up).
The official police statements make clear that there doesn't seem to be any kind of terrorist-related motivation and the descriptions of events certainly point towards some kind of psychological episode.
The truth will come out in time (though not necessarily on the front pages) but that will sadly leave plenty of scope of the trolls and opportunists to stir things up. Please don't play along with them.