This comes from personal experience in the USA. Never talk to/Interact with cops unless asked directly. Never call 911 unless there is a threat to life, risk

This comes from personal experience in the USA. Never talk to/Interact with cops unless asked directly. Never call 911 unless there is a threat to life, risk of serious imminent injury to you or to family. If you have to do it for a bystander, call 911 ANON & LEAVE. The chances of tracking you down if you are truly uninvolved are remote - OTOH if you hang around and expect a pat on the back.... The cops are generally working under totally different incentives than your well-being. A surprisingly large number are also Bullies and Thugs on a power trip. The best outcome is that you are left alone - the worst is ...well you can imagine many, many horrible things including loss of life.