If they were, the whole cop-killers, BLM, excessive use of force issue would not be an issue. The law would just say "Okay, a cop killed someone, that's their job, get over it." You can argue that the criminal justice system is too light on cops, but the fact that the criminal justice system is even involved means that killing people is not part of a cop's official job duties.
Practically speaking, law enforcement does have broad authority to kill people. So long as that death falls under the training guidelines written by the department, then it's unlikely the officer in question will face any punishment.
Now, killing a person might be seen as a violation of their civil rights, entitling their estate to compensation for the death. But that's a punishment for the state, not the individuals involved.
Law enforcement individuals have extremely limited authority to kill people, exclusively(?) based on self-defense.
The law enforcement system has the right to authorize the killing of people but is subject to judicial review.
Ergo, if a law enforcement individual breaks guidelines and kills someone, they're charged.
If a law enforcement individual follows guidelines and kills someone, then the system is charged. (E.g. state/federal lawsuits, consent decrees, etc)
