Who was it, then, who was sitting on the passenger's side of the car and around Z-145 started leaning far to his right while continuing to look straight ahead?
Bennett is looking left in z145 but he is not leaning left any discernible amount. But he is a bit higher than Dave Powers (whose face appears to be blocked by the roof support bar and whose hair is just above it) and Emory Roberts in front of him. He is not as high as Hickey on the left rear seat. O'Donnell was in the left jump seat.

If Hickey and Bennett were looking at the crowd they would have to be looking directly to the side or rear because the two agents on the running board blocked their view of the crowd in front. The only way to see in front would be to lean out. So if either Hickey or Bennett leans out it is to look forward.