Quote
In the '60's Batman TV show, Batman and Robin were deputized members of the police force, but that worked because they were just cops with special gadgets and unusual means. They were subject to the same limitations as the other cops.

The people who write the Law and the Multiverse blog have a very interesting post about this. As they say:

Quote
Constitutional limitations on things like censorship, discrimination, and search and seizure do not apply to private individuals but rather to the federal government and, in some cases, to the states. (The Thirteenth Amendment is a rare exception that applies to individuals). As a result, evidence that a superhero obtains by breaking into a villain’s headquarters is admissible even though it was obtained illegally. See, Burdeau v. McDowell, 256 U.S. 465 (1921). And since it doesn’t invoke the fruit of the poisonous tree doctrine, any additional evidence obtained via the original evidence would also be admissible.

But what about superheroes like Batman who work in close cooperation with the police? Could they fairly be described as state actors, thus triggering a whole spate of Constitutional protections? I think the answer may be yes...

...(legal citation here)...

In Batman’s case, Commissioner Gordon is certainly a person for whom the State is responsible, and Batman often acts together with Gordon and obtains significant aid from Gordon in the form of information and evidence. Batman’s conduct is also otherwise chargeable to the State because the Gotham Police Department has worked with Batman on numerous occasions (and thus knows his methods) and operates the Bat Signal, expressly invoking Batman’s assistance in a traditionally public function. This suggests state action under the public function theory: “when private individuals or groups are endowed by the State with powers or functions governmental in nature, they become agencies or instrumentalities of the State and subject to its constitutional limitations.” Evans v. Newton, 382 U.S. 296, 299 (1966).

In the real world, this would cause significant problems for Batman and Gotham. Batman’s rough and tumble style would lead to a rash of Section 1983 claims for damages and probably also for an injunction against Batman’s future cooperation in police investigations. As discussed earlier, most evidence that Batman collects would be inadmissible, and police use of that evidence might bar the use of additional evidence collected during a subsequent police investigation.