Sorry for the initial insensitive joke...If I am reading this correctly it sounds like the person who allegedly threatened to shoot you is some sort of regular in your ER. If your ER is like others, say Harborview in Seattle, there are no doubt some crazy folks hanging out along with the uninsured elite (sic). Basically a hotbed of losers who may or may not be responsible for their actions.
What is missing is some context. Why did this loser pick on you? Perhaps you routinely try to make him go away and he tosses some faux threats your way to shut you up>? Can't tell from your account. Perhaps the cops are jaded from seeing the same junk every night? So they don't take it seriously.
As one who has had a 9mm pressed against their head I can say I know the difference between a real threat of death and the hackneyed threat that I have also heard...something like this: " Shut up fool or I gonna put a cap in yo ass...." Cops have a tough job and maybe they spotted the phony threat for what is was and you took it too seriously...Like I said without a real context it is hard to tell.
A lot of victims will tell you that the perp gets the slack while the victim gets ignored...Thanks to the liberal ACLU inspired view of justice...Perhaps the cops have been accused by ACLU types in the past for being too quick to jump on a poor misguided sole who was just acting up. Perhaps they have been drug into court time and time again only to see the perps walk on some ACKU inspired loophole?
Of course had I been assaulted by some loser who threatened to put a bullet in me I probably would have busted a cap in HIS ass and I would be in jail and he and his lawyer would be rich.
Maybe running to your union will work? Maybe you should call the ACLU and see if they want to sue the cops.