If his intentions were to kill from the get go, as it seems you and some others are suggesting, then he had plenty of opportunity before he actually did shoot.
He was yelling out the code word "HE'S REACHING...HE'S REACHING!!"

At that point, he could have just shot him and probably could have gotten away with it.
But he doesn't. He shows some restraint and keeps issuing commands.

It's only when dude tries to get out of the car against the cops orders when things turn tragic.
The cop is actually fighting him trying to keep the door closed. And when he makes it out, he shoots him.