<human>: So my girlfriend and I came home from a day of visiting family only to find a small bag filled with a few scraps of paper in it (envelopes with our address and names on them) hung up on our doorknob and a threatening letter saying "What the fuck is your garbage doing on my side? Do not do that shit again or else." written in all caps and signed by the superintendent for the building next door (owned by the same management company). I went down to speak to our super about the issue and he was sympathetic, telling me that he had spoken to the other super about the issue and that he will make sure to speak to him again and let him know that he can't be writing things like this to tenants.
My issue here is not only did someone hired by the building management leave an extremely unprofessional note on my door, but he also threatened with 'or else'. I can only assume that 'or else' could mean anything. I plan on calling management on Monday to chew them out about this, but I've been letting my mind wander at what the threat could possibly indicate. He has keys to the building after all. Should I make a copy of the letter and bring it to the police? I feel like that might be an overreaction but honestly I'm not willing to risk it. We love our apartment and don't want to move but now we're starting to feel a little unsafe, and all over literally one small bag of garbage that somehow wandered to his buildings trash.

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<bot>: A small bag of our trash was found in the building next door's trash area and the super wrote us an extremely angry and threatening letter. What do?