I live in a part of the world where total closures are pretty standard for 2-3 months a year. Other areas are closed off more permanently.

There are still shitloads of people there. We sometimes get special permission to train in closed area and we love it because it should be an uncontaminated area, but I'm not sure I've ever had a training weekend in a supposedly closed (and well-publicized; they're closed due to danger, not for our trainings, we just get special permits because they trust us) where we haven't found a "lost" hiker (bull-fucking-shit they were lost, the entire range is closed and it's publicized all over).

Even when it's so severe that we can't even get permits, I've heard from a few ranger friends that it's still common to find hikers and recently abandoned campsites (still smoking, often, which is especially bad since in my area we typically close due to fire danger).

So I guess, never underestimate the number of illegal hikers in an area. Murder isn't impossible, but it is pretty unlikely in my experience, while illegal hikers are obnoxiously fucking common (seriously, y'all, if it's closed, it's closed for a reason so stop ruining things for the rest of us).