A work colleague, who now feels overwhelming guilt that he didn't see the signs, described him as a man who was not happy with life and who was constantly and obsessively railing against Jews, homosexuals and other groups in highly-abusive terms. His ex-wife described him as violent, controlling and abusive. The FBI has interviewed him twice but not followed up. The US President says that there is no evidence that he has been guided to this action from outside. He is a US citizen. No- one can argue that this wasn't an act of terrorism. But this is not the time to indulge in kneejerk attacks on Islam.