No they couldn't. That would be equivalent to saying committing a crime creates a right to privacy that didn't exist previously. And if it wasn't part of their official duties, why would the department/police union be defending the officer?
You do sometimes see cases where a police union defends an officer accused of some crime, but that's usually because they're putting up some BS story about how they actually were doing their duty, eg an officer busted in possession of drugs who tries to argue it was actually an undercover investigation of the drug scene.
You do sometimes see cases where a police union defends an officer accused of some crime, but that's usually because they're putting up some BS story about how they actually were doing their duty, eg an officer busted in possession of drugs who tries to argue it was actually an undercover investigation of the drug scene.