I take it this is a rhetorical question. PMSNBC has stated that there is "no information" regarding the shooters' motivation.
Some people, such as myself, suggest the fact that he changed his name to Muhammed might be a clue.
To me, the fact that he changed his name to Muhammed in 2001, after being a practicing Muslim since the eighties as plain old John Williams, is even more telling.
He was picking a side.
Islam is based on violence and hatred for every other religion, especially Judaism and Christianity. No wonder Hillaire Belloc sounded the alarm about 'Mohammedans', particulary in regard to their invading and populating Europe. Now they're here and we will soon find ourselves in the same types of situations as does Israel - suicide bombing (WTC), assassinations (sniper), violence, mayhem, etc. It is cleary time to quit pretending otherwise and face reality!