Welcome to the new matrix. I've just acquired various cams to monitor my property and as long as I'm not in view or hearing, I'll make it public in a heartbeat, as appropriate.
They do own the evidence, but "voluntarily" surrendered it to law enforcement. If they don't have a copy, then that's that; meaning they can't produce what they don't have. At some point they get their property back.
As for having video available for the general public, certainly there is no duty to provide that, even if the requester is willing to pay for it, and there are good business reasons to keep your recordings as your (private) property, subject of course to judicial process as is all evidence.