are cops allowed to kill criminals deliberately??i mean deliberately aim head and so on?

If you shoot, you shoot to kill. Otherwise, you shouldn't be shooting anyone.

Yes if the criminal is a threat to their lives or the lives of others. In the UK at least, anyone wearing a suicide vest would be shot in the head to immediately incapacitate them and prevent them from detonating it.

Yes.

If you start out aiming for things like hands or feet, not only have you failed to stop the threat, but you've put the public at risk should you miss.

You aim for the big center mass.

The purpose of shooting someone is to stop the threat. If you shoot someone in the leg, they can still shoot back. That is why officers are trained to aim for the center of the chest or the heat.

Yes.

No. There families sue & win often. In America that privlige is reserved for the good citizen. To keep them in fear of what the cops on the street are.

If ANYONE is legally justified in shooting someone, they are legally justified in killing that person. In reality, shooting to wound is BS. You are more likely to kill YOURSELF than to stop a threat by wounding someone you are shooting at.