Strange case. I know fatigue can be dangerous while driving, similar to being drunk. Entering the wrong apartment seems possibly if very tired or distracted, but wouldn’t she have quickly realized the furniture was different? Poor guy, what a tragedy for him and his family. Why are cops put on administrative leave pending an investigation instead of arrested like us civilians? Honestly asking.
I think the administrative leave is separate from arrest. Arrest would be a criminal thing, whereas the administrative leave is due to their employment and they're often put on leave during an investigation phrase and prior to a decision on whether they'll be fired or not (if discharge of weapon was found to have been a legitimate accident vs manslaughter).