See, I smell conspiracy theories all the time. however, I think one thing stands out that says it might NOT be... The fact they don't have a patsy all ready.
48 hours after a bombing with dozens of cameras on it - they haven't released squat for blame. they are actually asking for video, and maybe looking incompetent.
I tend to lean to this really being a random attack by one or more people... They're downplaying it as much as possible to avoid looking incompetent.
I think this was an actual attack, and they haven't figured out who did it, to be honest.