Continuity mistake: Steve McQueen passes the same green Volkswagen at least three times while chasing the black Dodge Charger R/T. This is due to the same downhill portion being shown to us from multiple angles to artificially extend the length of the scene.
Continuity mistake: Bullitt runs the Charger off the road into the gas station. The station explodes...Right? Not quite.... The Charger runs off the road, passes BEHIND the gas station; you can see the dust trail rising; and boom, the station explodes on cue.
Continuity mistake: The gray-haired hitman enters the hospital in the dead of night. He ends up being chased through the building by Bullitt for about 10, maybe 20 minutes. But when he safely flees the hospital, we see plenty of bright, morning sunshine.
Continuity mistake: There are three different views of the strangled Mrs. Rennick. 1. Cathy looks down on the body on the floor, after entering the room and leaving the door wide open - notice between the victim's face and left hand that there is nothing on the carpet. A policeman moves his shoes enough to be seen close by her hand, too. 2. A flat black object appears beside the victim's face. The black shoes are now missing. 3. The last view shows a close-up of the object and a clear view towards the door. A policeman and Cathy should both be seen in this view, but they are missing and the door is now closed. (Don't confuse this dark object with her fat, round hair curlers. They are noticeably different lengths and shapes.)
Continuity mistake: During the chase scene, mainly in the city, the shadows are inconsistent. For example, at the beginning of the chase, Bullitt makes a 180 turn and climbs a short hill, losing the Charger. When the Charger is climbing the hill, the street is in bright mid-day sunlight. After a cut to show the driver's face, the next view of the street shows the houses and street in very different lighting. This is not the only example that shows different shadows, either.
Continuity mistake: During the chase, when Bill Hickman drives the Charger into the residential area, as he loses Bullitt he comes to a distinctive intersection: he first looks right, then left. As he looks left, the first view of the sky shows it is half full of light clouds. A moment later, when the car drives on, the sky is completely clear of clouds. There are other shots showing even heavy clouds/blue sky, too.
Continuity mistake: Changing speed: in two shots of the Mustang during the last of the chase scene, the car's speed changes. As the camera pans with Bullitt's car, passing the gas station on the highway, we see the first explosions, and his car seems to be going about 30-35 MPH. Then, as the car skids across the median into the ditch, the Mustang looks as if it was initially going at least 50% faster.
Continuity mistake: Bullitt parks the Mustang, and when he goes to interrogate the cabbie, there is dirt on the body of the car, behind the left front wheel. The Mustang is clean in all other views of the car, after this parking lot scene.
Continuity mistake: It's well known that two different '68 Fastback Mustangs were used to film Bullitt. The two cars can be seen by watching for the driver-side mirror. It looks as if the re-enforced stunt car had the mirror. The other car can be seen in the night scene, when Bullitt rushes to his shot partner, at the hotel. That car has no mirror on the door.
Continuity mistake: During the famous chase scene, most shots of the Charger show its rearview mirror where it normally should be, attached on its arm, above the windscreen. At the point when the Charger crests the "stepped" hill, though, the hitman briefly flashes his left hand in front of the camera lens, but there is no mirror. The mirror was obviously removed to improve the view.
Continuity mistake: Gunshot windshield: the hitman shoots the Mustang's windshield with a shotgun blast. The passenger-side of the glass is now damaged. In the very next cut, the camera has a straight view through the Mustang, showing the passenger side of the windscreen is not yet damaged.
Continuity mistake: During the operation room scene, Dr. Willard's forehead is visibly sweaty. A moment later, his forehead is not sweaty, but he has his forehead wiped anyway.
Continuity mistake: When Bullitt parks his car at the carwash, the front wheels are turned sharply to the left. When Bullitt approaches his car, after he finishes with the cabbie, the wheels are in a neutral position (straight).
Continuity mistake: During the lengthy downhill portion of the car chase, we see the Charger and the Mustang pass the same white Pontiac LeMans at least three times, due to the same moments in time being shown to us from multiple angles in order to extend the chase sequence.
Continuity mistake: In the leadup to the chase, the Charger stops at the top of a hill and the occupants look left where we see a green car parked in front of a red car. As the Charger pulls away we get the same view. The red car is still there, but now has a blue car of a different model in front of it and in a different place.
Continuity mistake: During the chase on the hill, the Charger loses a hubcap while making a left turn (in the only shot when the yellow cab is visible beside the Cadillac). When the same location is shown, but from the opposite angle, the hubcap is not visible in the different take. The hubcap should be rolling in front of the Mustang, as it closely follows the Charger.
Continuity mistake: The Charger loses three hub caps during the chase but has two still on it when it crashes into the gas station.
Continuity mistake: In the scene were Bullitt and Cathy are talking by the roadside, we get a front view of her as she raises her hand to her head and she is holding a yellow flower. Cut to rear view of Cathy - no hand or flower. Back to front view - hand and flower are there again.
Continuity mistake: During the the car chase the Dodge Charger loses a hubcap going down the hill from the far side of the car. The other hub cap from that side comes off when the Charger hits the wall on the bend, but when they join the freeway only the front one is missing.
Continuity mistake: In the interior forward shot from inside the Charger as it goes down the hills and we see a white Saloon pull out from a side street and turn right and the charger passes this car. Then we cut to a view looking up the hills. We see the Mustang leap and the same white Saloon is again pulling out of a side street and turning right.
Answer: Notice: Aprea is credited as "Killer", not "The Killer." I think this confuses reviewers, as they assume he must be one of the hit men. However, the hit men are credited as "Phil" (Bill Hickman) and "Mike" (Paul Genge). Genge is much older than Aprea and Aprea does not look like the grey-haired hit man, as another contributor has pointed out already. There is no other killer in the plot. Perhaps Aprea's scenes were cut.