In this instance, it appears the shooter was a nutcase radicalized Muslim. The Fort Hood Shooter was a mental case Muslim.
What they don't share in common is that they were Muslim. It's that they are nuts.
If you wish to remain oblivious to the fact that Islam is a special danger, be my guest.
It's a variation of "All Sikh men are named Singh but not all Singhs are Sikhs". All muslims are nuts but not all nuts are muslim.