Pretty fucked up situation.
At first I was OK with the self defense thing but as the story evolves, it sounds like the driver/shooter was unjustified in his actions. If it's true that there was no pipe then it's time to charge him with murder. Cops accidentally shoot people under similar circumstances from time to time. "I thought I saw a weapon" is all it takes for them to walk free.
If you're gonna shoot, you better be damn sure and not pull the trigger because you panicked.
Years ago a man got out of his car at an intersection and started beating my friends car with a wooden broom handle. My friend started yelling at me to shoot him or at least flash my gun. My response to my friend: "Ya know, you could just turn right and keep driving." My friend's mirror got busted up but none of us got killed, hurt, or went to jail that day.