He did not drop the gun until the guy in the dark shirt whacked it with his left elbow as it looked to me. I am betting they were cops and the guy who ran out either an accomplice or an informant. The guy in the black shirt and other guy to the viewers right (who also puled a gun) were aimlessly milling about, the guy in dark shirt even looked out the door as if waiting for it. Other guy who bought something and took forever to draw, a cop who should be retired already or on a desk job. Of course that is all just conjecture on my part.
Brought to mind the NYPD's Stakeout Squad of yesteryear.