Boom boom is right on the money. We have a sworn officer acting irresponsibly with his duty weapon, in a mental health facility, and threatening to shoot a psychotic patient. Is that about the size of it? I'll tell you right now, if he worked for me, I'd snatch a knot in him the size of which it would take a buzzard a month to fly around. It didn't happen on that occasion, but if he keeps this up, and I bet he will, he WILL provoke an incident. The problem is that when he DOES provoke a response, you'll have MANY unbalanced people acting out, responding, at the same time. Bad gris gris as the Creoles say.
There is very little you believe that you can do to affect change in this gold plated nitwit, so your next best goal is to protect yourself and the patients in the facility. My first stop would be to stop by and have a little face to face time with your supervisor. Tell him what you've told us. Keep in mind if things blow up, your company may lose the contract, and I guarantee that your supervisor will face some of that heat internally from his boss. Second, if he finds out that you knew that this was going on and you DIDN'T tell him, you won't be his favorite employee, and we want to avoid that.
Your best options as I see them are
1. An anonymous complaint to his agency
2. A friendly conversation with your supervisor.
3. keep a diary of these things in case it comes back to bite you. Lawyers and investigators love documentation.
You seem to be the only responsible adult in the situation. Watch your back, be careful, and I hope this ends well for you.