Flock records public events. None of these apply. There is no reasonable expectation of privacy in a public space and the courts have been quite clear on this. Actual legislation would need to be passed to restrict what can be recorded in public settings. A redefinition of "public", basically. And what about the public? Would they also be barred from making their own recordings of public events? Would they be barred from sharing them with law enforcement?

Not necessarily. One could argue my cell phone's signal is in the public when I use it (home or otherwise; it is rather omnidirectional), and the records thereof aren't subject to it the same way as say a search of my phone or my home.

However, in Carpenter v. United States, government entities were found to be in violation of the fourth when accessing historical CSLI records containing the physical locations of cellphones without a search warrant (at least over a period of 7 days or more, if I understood it right). Previously, it was considered fair game under the basis of records technically turned over to a 3rd party.

Then there's United States v. Jones (2012), where it was established a GPS tracking device was attached to a car constitutes a search.

It remains to be seen how Flock will ultimately hold up in court. Although a few cases have popped up, I think it's too early to tell.

The police officer is not standing on the street corner, observing public events. They are searching a privately-held database of sensitive information whose use is governed by certain restrictions, which are being violated by the police officer. Whether or not those violations rise to the level of crime does not erase the fact that they unethical, and likely against both Flock's terms of service and the department's policy.