Hm. Honestly, if you’re not willing to get police involved, the only real option you might have would be to confront the person you suspect. Obviously they may be a danger to others, so you may wish to do it in a very public space where you can put something physical between the two of you (eg a restaurant table).

If it were me, I would maybe take one person (at post) with me if I really felt threatened by this person. But by all means, don’t make it a huge deal or you will spook or freak out this person. Best case scenario is they flee and stop posting and then you won’t know what they’re up to. Worst case is that they flip out and decide to go in their dream rampage.

Short of that, I would also strongly recommend that you and your friends always stay in groups of at least two (maybe three if possible). Maybe pair a friendly guy with a girl (if they are comfortable with that). I suggest that because the stalker probably would be intimidated by the male presence.

All of that aside, go to the police. Even if they are incompetent, you must get this documented as soon as possible.