Cops can politely ask owners of private cameras for access for things like murder investigation. If the polite answer is no (most people will say yes), they can go to court for a subpoena. This has happened for a long time. This is how it should work. If the cops are too lazy or chicken to ask a judge while investigating a murder, they don't deserve the footage.
This was exactly the case on a King County jury I was on. Lots of camera footage, most from security cams of individual businesses, some from red light cameras.
The event predated Flock rollout though, so no idea if the distribution of camera sources has shifted.
Regardless though, in the end the phone location data meant a lot more than any of the camera data, which just confirmed the path from phone sources.
Right and what if lots of crime happens in a place where there are not many businesses? Hardly an implausible scenario given that crime is bad for business.
The city can set up its own camera for its own use. Is that really that wild of a proposal?
This is very doable when what you're dealing with is a Major Crime That Gets Full Institutional and Individual Attention.
What about a bike theft, a jacked car or a stolen parcel though?
There is a price to having information easily available to the law enforcement. There is a price to not having this information easily available to the law enforcement too.