I'm glad that you shared that with us.
I've had two relatives who made serious plans to murder others. The first was related by marriage. This took place when I was a young man. I did not think in terms of using "the system" to try to prevent this cowardly dog from going through with his plans. Instead, I relied upon the only language I knew -- and communicated in such a manner that he moved away from our area. When I've told my sons about that chapter of my life, they were surprised by my ignorance. Luckily, and only by luck, the coward moved out-of-state. (I still have some of the weapons he had gathered in his basement. He had made a map of his work-place, with stars for where he intended to kill co-workers. He planned to kill his wife and children first. Looking back, I am amazed that he didn't kill anyone.)
The other was my very ill brother. He was a violent man. At this point in life, I had a grasp of the system. It was curious: there were several times when I was driving through the town he lived in, and was "pulled over" by police. Not for speeding, or any infraction -- but rather, for cops I knew to ask, "Can't you do anything about your brother?" In fact, I had tried several times -- with the help of one sibling, and the opposition of another and our mother. It definitely fractured my extended family system far beyond repair.
There was a series of psychiatric hospitalizations, times in "detox" and rehab, and stays in jail. As his mental capacities declined, his level of threats increased. And those who deal in very large quantities of various white powders often access serious weapons. At one point, he had a gun that could take out 12 people in seconds. With the assistance of an uncle, then retired from law enforcement, it "disappeared."
I can't count the number of times my sister and I sought help from "the system." Yet, even the police are sometimes handcuffed in their ability to deal with potentially violent individuals. Luckily, nature took its course. Though my brother is still breathing, he poses no threat to anyone. I see him once per year; sometimes he recognizes me, other times, he doesn't.