Police have the right to defend themselves if they fear for their lives. It was terrible accident indeed that could have been voided if he'd not physically interfere or have a gun on him.

Defend themselves from the already pinned down person that never drew a gun by shooting him to the back of the head?

Think about what you're saying. You're trying to defend the indefensible.

Police heard a gunshot and pulled the trigger by accident. Hence unfortunate accident.

Pulled the trigger by accident eleven times???

Come on man, don't debase yourself like this.

Yes, police are trained to always fire multiple shots at threats.

Again, not police. Armed goons.

They don't stop being police just because you want it to be so. You can tell yourself that, but the government disagrees with you.