I can see that, but I still think in both cases, the forces of order (and here I would include every able-bodied citizen as well as the police) should assist each other to the extent possible.
The crazy part is that a person in the commission of a crime assaults a responding police office and I render assistance which results in the bodily injury of the assailant, the assailant could probably find some lawyer to sue me for damages, and, depending on the jurisdiction, would probably win. In southwestern Virginia, such a person might get another butt-whoopin' just for filing such a suit, but in the lost portions of the state where the ausländer preponderate, such a suit would probably result in damages being awarded the assailant.