I'll just briefly add that I've spoken to a number of people who have received these duties to warn. You are visited by law enforcement. You are given a piece of paper to read, which is then taken back. You are not told what the source of the threat is. You are not given any real resources to protect yourself. You are told that you must change your routines and take precautions, but what those precautions and changes to routines would look like is not clear.
These people feel abandoned. They feel a little bit helpless and they feel stigmatized. If this information goes out into the community, they don't want other people to know, necessarily, because then they won't feel safe being around in those same spaces.
It's a very unsatisfactory process. I'm not sure how much it actually helps.