Undercover agents are police who work undercover to investigatecrime and are totally different from little security informants.
警察从事秘密的调查活动才叫卧底，完全不同于治安小信息员。
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This you-are-there guide takes you deep into the world of crime, giving you a better understanding of the dark recesses of the criminal mind and how law enforcement officials investigatecrime.