take the law into your own hands

Từ điển Oxford Advanced Learner 8th

take the law into your own ˈhands idiom
to do sth illegal in order to punish sb for doing sth wrong, instead of letting the police deal with them
•After a series of burglaries in the area, the police are worried that residents might take the law into their own hands.
Main entry: ↑law_idiom