citizen's arrest
noun [ C ] uk/ˌsɪt.ɪ.zənz əˈrest/ us/ˌsɪt̬.ə.zənz əˈrest/
公民逮捕（普通民众发现罪犯后自行扭送至有关机构）
an arrest made by an ordinary member of the public, not a police officer
You can make a citizen's arrest if you reasonably suspect someone of committing an offence. 你如果有理由怀疑某人犯了罪，可以实施公民逮捕。