COPS (TV show) How Do They Obtain Permission?

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I've always wondered, how does "COPS" get permission from the perp to show them on TV?? I mean, some of these guys must be pretty stupid to sign waivers.

I love how it's like the cameras aren't even there. The perp lies, despite the camera catching him in the act.

[20Truck 7]

Technically, do they really need permission? Im going to guess in certain situations they don't actually need permission... ie. public property. Others...Im not sure.