If the police have seen the surveillance footage, and are now saying that they're out of leads and don't know anything about where Paighton might be, that can only mean they've already checked out what's on the footage and it didn't lead to anything. In that case, if they release the footage to the public, all they risk doing is getting two "heavyset" black guys (where did this information come from, by the way? I'm still not clear) in trouble with the people in town.
I mean, I guess it's possible this is all some sort of nefarious "hick cop" cover-up. Or maybe it's all some sort of swerve by the police to fool the "bad guys" into thinking they got away with it, only for an arrest to be made sometime soon. But it seems more likely that the surveillance footage simply doesn't have anything on it that will lead to Paighton. At any rate, from the way the cops are acting, it doesn't seem like they believe that releasing the footage to the public will accomplish anything.