> However, there is zero legal duty for the police to protect someone who is currently under attack from a criminal.

That has to be incorrect, by the time someone is under actual attack from a criminal that criminal will have allready comitted crimes that the police can and have to punish for, i.e. Threat of Force with a Lethal weapon or sth like that.

Legally, the police do not have to swoop in to stop someone who is actively murdering you. They can just wait until later and write a report after you’re dead.

1981 Warren v. District of Columbia