"The Departed Question" SPOILER WARNING?

Yes, Jack Nicholson WAS indeed an FBI informer...no trick...The police had NO idea he was an FBI informer...the police and the FBI had different agendas where he was concerned...and thus he was able to get away with murder.And yes, the two were quite tough towards DiCaprio...for several reasons...a)to see how he would react;b)to test him, if they could "break" him;c)and yes, to convince him he was MORE valuable to them undercover than as a regular cop...to overwhelm him with all they knew about his past that he had no choice but to acquiesce.