Gangsters use a very common trick to fool the cops, and they call it "rabbit run." Normally, a gangster (the rabbit) will start running after seeing an officer or law enforcement unit to divert the attention from the actual subject (drug dealer), and the officer may start chasing the rabbit. Yes, it can be difficult to determine who the "rabbit" is and who the concerned person is.
Prior surveillance can prove to be very helpful in these situations. If you have the prior information about what roles are assigned to the gang members, it can save officers from "chasing the rabbit" and catch the actual subject.