When interactions with police are dangerous (e.g. approaching police while black, or if you can be prosecuted for making an inaccurate statement) but the police still are capable of useful work, how to report crimes:
You tip them anonymously. Gaining anonymity can involve quite a few steps in modern society, and I’m not going to give a country by country breakdown, nor do I want to detail specific tactics without routine maintenance of this document, since the threats evolve. Here are the principles you follow:
– De-couple time. If you just drop a letter in the subway, the security cameras will have enough historical footage to pick you up. Of course, you can’t do this if you think the criminals have high operational tempo/are on a crime spree.
– De-couple associations. If it’s not too sensitive, have a friend of a friend post a message through a sort-of-anonymous proxy like Tor. Then the police have to do some work to trace it back.
– Don’t use voice calls. If you go with a letter, use a new pen that you throw out and don’t use your normal script or word choices. If you need to type it, type it in one place and send it in another place, using proxies or other things that make it tough for them to pull network records or security camera footage of your face, motor vehicle, etc.
– Printers are dangerous for a lot of reasons. If you need to type it, you already are taking a risk by using a computer, so don’t give the authorities another way to find you.
If you need to go testify, you don’t really have any options – you have to decide whether it’s a risk worth taking.