There is much speculation going on about the Ft. Hood shooting. The latest report says that soldiers heard the shooter, Major Hasan, yell "Allahu Akbar!" before he started firing. There are basically three possibilities, none of which has been ruled out.
1. Hasan was just a lone maniac who happened to be a Muslim. This would fall under the nuts do crazy things category, that is often the best explanation for murderous rampages.
2. Hasan's actions were motivated by his religious beliefs. For example, he might have felt that the U.S. wars in the Middle East were wars against Islam, or had other religious-based beliefs that motivated him to carry out the shooting. From what I have seen, there may be some evidence supporting this scenario.
3. And finally, Hasan might have had actual connections with radical Islamists. So far I've seen no evidence this was the case.
Since Hasan is alive and in custody, not killed in a shoot-out as originally reported, an investigation should be able to uncover the details and find which of these three scenarios applies.