“I would have called the police, that night, and reported that he was dangerous.”
And they would have said, “We can’t do anything. No law has been broken”.
You are wrong. A law was broken. He was a felon in possession of a firearm. And it was a stolen firearm.
But you miss the point entirely. Even if the police did not do one thing .. I would have done what I could. I don't care if ten people behave irresponsibly ..so long as I do the right thing. Now do you get it?