We had a neighbor who was paranoid schizophrenic. He heard voices, he wrote all over his truck and his interior walls, yelled at people. The cops tried to avoid dealing with him. The internet was a very bad thing for him. It turned out that he had guns, but he never did anything violent. We were lucky. But having seen him do his stuff for years, I can definitely see how this kind of person could snap.
One time I was walking our dog down the road and he was inside his tree line, using a chain saw. He saw me, revved up the saw and yelled, "I'll see you in hell". He was probably trying to be funny, and it was, but it was also not. We didn't get along but I knew better than to confront a crazy man, even when he didn't have a chain saw. I tried to stay out of his way. I also tried to get the cops and other agencies to get the man some help before something bad happened. But they didn't want the hassle. Hell, one time I saw him shoving the deputy who had come because of a tow truck dispute. They still didn't arrest him. It might have made a big difference if they had.
Eventually he stopped eating or something. Probably didn't trust his food, who knows. I hadn't seen him for weeks. I did a welfare check, found him near death and called 911.
Through the window, you could see him laying on the floor like he was dead. I had to convince the ambulance guys to go in because they thought he could be playing possum and hiding a gun. I pretty much had to shame them, it was kind of disgusting. Eventually he was nursed back to physical health and is living out his days in a long term care facility. He is probably 70 ish by now.
I had a number for his sister downstate. I called and told her the house needed to be taken care of etc. She wanted nothing to do with it or him. Said the family was scared of him. I suspect that's a common problem in these cases.