I agree with the people here...
Do whatever it takes to prevent his taking further action on this. The Army taught us to accomplish the mission, and take care of your troops. I see your mission here as preventing him from killing himself, but that's just my opinion. I dont know how I would live with myself if someone I knew & cared about was in this situation, and I didnt do all that I could to prevent him killing himself. Its a hard place to be.
Just another thought, but the Lord Jesus Christ has the ability to change people. Prayer really DOES work.
If your friend is in a place mentally/spiritually where he WANTS to inflict pain on others, that's really an indicator of the pain he is feeling. Hurting people often want to lash out & make others feel what they are feeling.
But now, please allow me to offer another perspective:?
As a Christian believer/preacher.
Enemy activity 101:
Human beings are a spirit, with a mind/soul/personality, that live in a physical body. Humans have the ability to hear/see/perceive/feel spiritual influences. The enemy(Satan/the devil/demons) have the ability to speak to people. God/Jesus/the Holy Spirit/angels also speak to people, and we have the ability to hear/feel/perceive this.
The enemy seeks to steal, kill, & destroy human life. He steals what God wants to do in peoples' lives, kills them physically, and then they are destroyed spiritually in hell.
People report that "the devil made me..." do this or that. One very basic maneuver the enemy tries, is to influence a person mentally. He will sometimes tell a person, "you're depressed" or "you need to kill yourself" and the person is shocked! because nobody WANTS to be depressed or suicidal. Often, that person then starts "owning" these negative thoughts, and the process of growth begins. The thought becomes an idea, they dwell on it, and it becomes a plan. Then they take action & it becomes a reality, and bears fruit in the end: they become depressed, or attempt suicide.
Now IF, on the other hand, when those kind of thoughts come into their mind (some people report actually HEARING voices) the targeted person says, "Fuck you, that's crazy. I'm not having it!" it can nip those VERY REAL thoughts in the bud.
I'll give you an example. In fall 2016 I was doing something outside & I was MAD at everybody. Mad at my ex-wife, my kids, my friends, the people at church. And I didn't WANT to be mad. I asked myself where were these thoughts COMING from? And it was like the lightbulb went on & I realized that these thoughts of anger were being imposed upon me from a source OUTSIDE MYSELF. A real AHA! moment for me. I was being influenced to anger against my will! Nobody WANTS to be depressed or to kill themselves. In my opinion, as a preacher, people are being played by demonic forces, against their will, and often without recognising it, nor recognising the true source of these very real, very negative thoughts.
Lots of people believe in the existance of the spirit world, because they have had personal experience/evidence of it. If a person is a fighter, when you present a target to shoot at, they can then rise to the occasion and begin actively resisting it. Evil/dark spirits can be identified by what effect they have on a person. And they OFTEN, ALMOST ALWAYS operate in packs or gangs.
I cant prove the spirit world exists (God, Jesus, angels vs Satan, demons, etc) and you cant prove they dont. This is just my world view. Just one guy's opinion.