4.

vigilante
治安維持會

[雙語解釋]

A person or group who takes the responsibility of a law enforcement officer into their won hands.
承擔(dān)執(zhí)法人員維持治安責(zé)任的個人和群體。

例句：

The subway vigilante in New York was in the media for weeks.
紐約地鐵治安維持會幾周來受到了媒體的關(guān)注。