Still from that Magic Moment at Dealey Plaza

Ignore the top of Kellerman's head, oily is his hair and and reminiscent of a barrel. Similarly, don't fall for that being Greer's arm pointed directly back in what would be a caricature of the motion required to make the shot. It's not his arm. You can trace it all the way back to the end of the car so it's a panel.

I maintain there is movement regarding the driver's hand and since the limo is not turning, his hand is doing something else (see video by scrolling down on this blog). However, even if that is his right hand, and it actually is on the wheel, that would be required to maintain proper direction for a speedy getaway immediately upon firing. If he is leaning back, the shot HAS to be being made with his left hand or he has to turn COMPLETELY around and it is a point blank shot for a secret service agent who, I'll warrant, is no novice.

Whether or not his right hand is on the wheel doesn't even come to bear on this conclusion.

You can see the line that is Greer's knuckles and the distance between the knuckles and the front of his hand is farther than the distance between the knuckles and the part of his hand that is toward the rear of the vehicle. Unless his fingers are all distended directly forward and outward, he isn't holding the wheel. If his fingers were wrapped around a gun, knuckles folded over, they would be behind the part of his hand that is between knuckles and wrist if he was firing toward the President. IF his hand is folded closed, it is pointed backward.

Looks to me like his right hand is on the wheel and his left is pointed backward.