Terrorists? Doubtful. Hate criminals? Unlikely. My guess; this was done by Beavis and Butthead -- i.e. bored teenage death metal fans, the kind that like their musical schlock served up with black leather, pentagrams, and quasi-fascist imagery. You know, bands like Slayer. That's Slayer, the same group that released an album called "Reign In Blood" back in the '80s.
Incidentally, yesterday was "the National Day of Slayer", a day proclaimed by one of the group's fan clubs and dedicated to the band and its "music". Coinicidence? You be the judge.