Don’t issue threats but like most things you should start with the basics if you can, many folks don’t want to go to police as it’s a hassle, fear it may really escalate things, and they don’t want to have their name on any public record. I always think in order to ‘make my problem go away’ you should try the ATM method a security guard told me he uses: Ask them, Tell them, Make them, using whatever is appropriate, lawful and will lead to getting the problem resolved.