Get bent. I knew a kid that threatened to shoot up 26 individuals and had firearms. My best bud called the cops and they intervened. Mind you this kid was out friend and we knew he had issues and was spiraling. He did not get in any real shit for that but later got felony charges and can no longer own guns legally. Yes when people make threats and have the means to follow through , and is killing animals for pleasure something has to be done. This is real life, not a fucking joke and op needs to hear this before they end up a potential victim. There is a reason their asking for advice and going to therapy and it's because their in a dangerous situation that needs rectified. And fyi I do not watch serial killer documentaries, honestly not huge on TV in general. I'm beginning to wonder if you identify with the person in question having reacted the way you have, or maybe your in a similar boat to op and afraid to take the first step. Trust me things can be made better if you are willing to try to do something about it, perhaps if the brother gets help sooner than later they may never go down a dangerous path. Either way intervention has to happen.