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.
Continuity mistake: During the Charger/Mustang chase scene you see Steve McQueen's Mustang skid around a lot of corners. If you look at the street you can see the skid marks from the previous takes.
Continuity mistake: During the chase scene where the Charger crashes into a parked white car, the screen blinks red to give the illusion of a strong impact. However, after the split second blink is finished, the car magically repairs itself and the Charger completely disappears.
Answer: The man shot at the hotel at the beginning is Renick. Ross assumed Renick's identity and was going to flee the country. Ross kills Mrs. Renick to keep her quiet. The man at the airport that Bullitt kills is Ross.
ChiChi