The view of a retired assistant chief of the Los Angeles Police Department: It was not a matter for the police; it was a civil matter between UAL and the seated passenger.
Makes me wonder who will pay more, UAL or the City of Chicago?
FWIW, my wife has seen a lot of people interviewed on the street by Los Angeles TV stations who all say they will never fly UAL again. My wife takes that at face value. I don't. A month from now, or whenever, most of the Internet savvy folks will book the cheapest fare on-line, whatever carrier it may be. I'm speaking of the occasional traveler who is not a member of a carrier loyalty program.