I don't know what or even if there are answer choices for this, but it sounds an awful lot like a <u><em>vigilante.</em></u>
Explanation:
From what I can find, the definition of vigilante is "a member of a self-appointed group of citizens who undertake law enforcement in their community without legal authority, typically because the legal agencies are thought to be inadequate". So, not exactly the same, but it sounds similar.
