I heard today that it was unlawful for a 17yo to possess the weapon he had. If that's the case, I believe he's fighting an uphill battle and put himself in a bad situation that he shouldn't have been in.
Such laws are considered suspended during emergency conditions (e.g., an earthquake), and riots would arguably qualify. Declarations of emergency aren't required for this legal exception to apply, only that a jury agrees that an emergency situation existed.
