During the stakeout, the detectives are in two different vehicles. When the gun thug shoots the informant from his car and drives away, none of the detectives use their vehicle to pursue the car.
At 6.13-6.14 while they walk down the stairs the camera pans up a little bit causing the mic to show.
Several references are made describing the race of a suspect as African-American. That term denotes ethnicity, not race, as it is possible to be a Caucasian from Africa that now lives in America. Additionally, black people in other countries are not called African-Americans when referring to their race.