Under US law, that cop is a criminal, operating outside the law, and at point a citizen's arrest is legal.  Of course the illegal and tyrannical shit storm and persecution from the other criminal cops would make justice difficult if not impossible without a lot of dead cops; in self defense. Especially since most courts in California are unlawful, if not criminal.  This is why the militia exists. With a functioning militia, the police would be turned away and their hostage freed, or the police would escalate and lose. This is why they want to disarm us. This is why they hate the militia. This is why most all gun laws are unconstitutional.