O.M.G... and I laugh when he started talking with that voice... and well that face.
Anyway, Yes, Omar was a lone crazy guy. But like the FBI already said, he was radicalize later. And yes It could have been revenge, but his struggles with religion, been a closet gay, and his radicalization later on, made him do this terrorists act and swear alliance to ISIS. They should check his blood to see if he was HIV positive.