The only way Costello could continue to operate was to cooperate with the FBI and provide related criminals... the tape recordings were evidence to support the people he intended to turn over to the FBI like Sullivan the dirty cop (Matt Damon)... Sullivan's girlfriend was listening to the recording between Sullivan & Costello in the Porn Theatre. For the storyline of The Departed, go to http://en.wikipedia.org/wiki/The_Departed

Costello is an informant for the FBI. In addition, he is also the most wanted criminal in the States. However, I think it should be that a man who worked for the FBI should work with the States together in arresting Costello... The thing is, I don't know why this most wanted criminal who committed many felonies like Costello, can become a successful FBI informant .( I mean he did not pretend to , but seriously, he did so) Maybe I missed some details? but I don't think it makes sense.. . Could you tell me why? ... and XD~~~ where did I make mistakes my in grammar? Also can you make my entry appear to be more like native English please... (above all XD) In a lot of countries including Australia, criminals offer to be come an informant in order for a government to make more criminal arrests. In turn, The criminal gets a reduced jail sentence.

Sorry~~~, I dont understand... could you make a explanation for your sentence?

If I give an 8 to the Infernal Affairs out of 10, I'll then give the Departed a 5~6.