To be fair, this guy sounds like he was severely disturbed regardless of his religious affiliation. I mean was he this Islamic Jihadi fighting the enemies of the Ummah, or was he some loser who got involved in this because it provided him with the direction his life lacked? His past history, petty fraud and drug possession would indicate the latter; he could have become a White Supremacist and done this, a Communist and done this, anything.
One thing I will say, Islamic congregations really should be more selective with who they let in and realise that there are people who will want to convert as a way of running from their past lives (happens a lot in the Pentecostal/born-again sects of Christianity I've noticed) and that that really isn't a sensible reason to convert.