Vigilantism

Vigilantism was when someone hunted down a person who was a criminal, or at least was believed to be, and either assaulted, captured or even murdered the person.

Although vigilantes generally targeted bad guys, they were not viewed as heroes by many people, because they themselves had no legal authority to take them down.

Even Batman, despite the fact that he never killed his enemies, was often considered a vigilante for a time. His association with the Justice League of America softened the faces of some people, but still, others considered Batman just as bad as the criminals he brought into the legal authorities.

Some mercenaries and assassins may have committed illegal violent acts against criminals, but this was generally not considered vigilantism, since they usually were paid to commit those acts of violence.