Befriended a mentally ill person, I now fear for my life?

I befriended this kid last year, he sat in the back of the room, very silent. He was smart, but then I got to know him. I learned he is fascinated with knives and guns. He is a religious nut, he says he hates everybody who isn't a catholic and that they should be killed in a genocidal fashion. He brings knives with him to school for no reason, he's even brought a tomahawk. Last night, a friend of mine made a facebook group about cats, and he decided to join in. He began to post images of cats being burned alive, mutilated etc. Around 4 months ago, I was in the car with him and he saw a dead cat on the side of the road and literally opened up my passenger side window and made his maniacal laugh at the dead cat. He said cats are "the Devil's creatures and should be exterminated from this Earth." Oh, and his laugh is like that of a serial killer. I'm beginning to fear him, and I fear if he loves seeing animals being mutilated, and he carries knives with him all the time, I fear he may try that on humans one day or at least try to get me involved.