The thing I don't understand is why it isn't a felony for the police the disable the surveillance cameras! That alone should be a crime. I get that you need search warrants and protections, but you shouldn't be able to suppress the evidence of your work, since it's common for police to steal, plant evidence, or destroy property.
It is a crime, obviously. Things don't magically become crimes depending on the employer of the perpetrator - that's the whole point of "a nation of laws and not of men."
It's legal for you to arrest someone if you see them commit a felony. It's legal for you to arrest someone under a warrant if you are deputized by a Sheriff of the court (almost never happens, but legal). It's not legal for you, whether you are employed at a police agency or not, to vandalize someone's camera.