informer|informers

那个告密者向警方提供了关于犯罪团伙的关键信息。

The ___informer gave the police crucial information about the criminal gang.

警方依靠线人提供的线索破获了这起案件。

The police solved the case with the help of their ___informers.

卧底探员依靠线人来获取犯罪团伙的内部消息。

Undercover agents depend on ___informers to get inside information about criminal groups.