Continuity mistake: While Sean tries to prevent the jet from taking off, in the exterior long shots of the aircraft there are windshield wipers over two of the cockpit's windows, but in the exterior closeups such as when Castor brings Winters into the cockpit the wipers are gone. (00:06:35 - 00:10:20)
Continuity mistake: When Sean and Tito first drive the Hummer onto the runway, the jet is a mere short distance away, coming towards them. In the following shots, the distance between the Hummer and the jet has increased tremendously, for the ensuing drama to unfold. (00:09:40)
Continuity mistake: After Castor Troy is told they are being followed on the runway, there is a close-up of Sean Archer and Tito in the Hummer and the rear view mirror is gone. It is back in all the other shots. (00:10:00)
Continuity mistake: When Castor Troy opens the jet door, the wall behind the cockpit differs when he pushes Agent Winters onto the runway, and the rest of the shots. (00:11:20)
Continuity mistake: After the jet crashes into the hangar, Sean Archer runs up the back end of a police cruiser, whose three blue flashing lights are completely shattered. In the next shot facing him, when he reaches the car's roof, two of the blue lights have repaired themselves. (00:13:45)
Continuity mistake: At the airport hangar, after Castor reloads, in the close-up Sean is kneeling beside a crate with a large black/white SCI air freight sticker. In the overhead shot, when Castor Troy aims the gun at Sean, the sticker is gone. Debris also disappears. (00:15:35)
Continuity mistake: At the hangar, when Castor Troy is blown backwards in the turbo tunnel he hits the wire gate, and the metal bar, about 3-4 ft long, breaks off and begins to fall with him. Next shot, he lands on the floor, but the long bar does not. It just disappears. (00:17:45)
Continuity mistake: At the airport hangar, when Castor hits the wire gate in the turbo chamber, the top of his head is well below the metal bar. But, when the emergency shut-off is pressed, his unconscious body has sat itself up, because now the bar is at shoulder level. (00:17:50)
Continuity mistake: At the office, when Sean is given the bottle of wine for a job well done, the way the bottle is held, first by the assistant and then by Sean, differs between shots. (00:20:40)
Continuity mistake: After Sean looks up his son's file on the computer, and types "case closed" on Castor's file, he rubs his head with his right hand in the close-up, but next shot he is rubbing his head with his left hand. (00:21:20)
Continuity mistake: At their home, when Sean tells Eve that he has one last assignment we see his scar. At the Walsh Institute, before the surgery, there is another close-up of the scar, but it differs from the previous shot. (00:30:20 - 00:33:05)
Continuity mistake: After the surgery, when Sean (as Castor Troy) breaks the center mirror of the tri-fold mirror, what remains are the two side mirrors and white backing within the center frame. When Tito grabs him as he starts cursing, in these close-ups the reflections seen are as if all three sides are still intact. (00:37:15)
Continuity mistake: When Troy (as Archer) arrives home for the first time, he's walking around his wife. When he says her name, his right hand is held up. From a different angle as he moves to her right, his hands are by his side. (00:52:50)
Continuity mistake: When John Travolta's daughter slams her bedroom door in his face, from one shot it nearly closes, but in another shot he blocks it when it's still got a long way to go. (00:54:35)
Continuity mistake: When Troy (as Travolta) is about to defuse the bomb, watch the timer, it goes down too slowly for the time elapsed. It shows 1:14 and 28 seconds later it only shows 1:04, not 0:46 as it should. (00:58:45)
Continuity mistake: After being told that Pollux was released from prison, Sean Archer (as Castor Troy) shouts that he's Sean Archer, then grabs hold of the bars above him, with three bars between his hands. Next shot, as the guard's foot is on his hand, there are only two bars between his hands before he lets go. (00:58:50)
Continuity mistake: When Castor Troy (as Sean Archer) turns off the video-cam and walks into the interrogation room with Pollux, the Coke has two straws, but next close-up there is only one straw as he turns off the microphone. (01:00:00)
Continuity mistake: At Erehwon prison, during the cigarette incident, Sean (as Castor Troy) is knocked down, and while on the floor the side bar of his left magnetic boot breaks and the entire boot begins to fall off, but it's intact when he crawls to get the cigarette. (01:07:20)
Continuity mistake: During the prison breakout, when Dubov falls over the railing after being shot, in the first overhead shot he falls backwards, but next shot he falls forward (chest down). (01:11:40)
Continuity mistake: On the chopper, when Sean Archer points his gun out the window, in the shot facing him the window to his right is a double slide type. In the next shot, from inside the chopper, his arm is through a single window that flips down. (01:23:00)
Chosen answer: Although they were on the same side, Troy is currently posing as Archer, which means he would have to do everything that the FBI would expect Archer to be doing. The whole point of the raid was to take out Archer, as well as Troy's gang. He would have rather risked killing part of his own gang than risk exposing his identity to anyone else.
Casual Person
That doesn't really make sense. In the scene, he goes out of his way to shoot him and smiles while doing so, carefully and slowly. Was not a collateral damage situation. The question is why he deliberately goes out of his way to kill him.