Remember the lady who was killed in the passenger seat. The door entry hole was low and forward, it missed the driver and killed the passenger. This may indicate an upward traveling bullet based on the trajectory.
A gun could be rigged sideways in a trunk for example to fire through an aperature, similar to the way M&M fired from their trunk. The trunk acts as a sound suppressor. The driver doesn't need to wear earplugs, he just yanks a string or pushes a button.
Just a thought.
In case it's a team of shooters,I've considered pickup shells or just junk and trash in a pickup bed for the shooter to hide in.Even a solid seat and gunrest could be camouflaged for the shooter well enough that other close vehicles wouldn't see a thing even while the shooter is comfortably doing his thing.
I've got some older "workin'" trucks.One has so much rust on the beds outside skin that gunports cut out of the inside bed material would give a shooter a nice place to shoot from prone.It wouldn't change the truck's looks at all.
About anything in the back glass of a regular car would allow a shooter in the back seat to take his shots even while being followed.
Moh and Malvo were "extremely" stupid to be caught so quickly,I think.
TM,I believe you said on another post that shooters will be harder to catch when "trained" snipers start doing this.
I completely agree but I'm afraid of what nearly anyone could get away with if they put their mind to it and use common sense.