Complex sentence: He gets back to the officers' apartment where Aarfy has raped and murdered Michaela, but when the MPs come they do not arrest Aarfy, they arrest Yossarian for going AWOL.
Split into simpler sentences: He gets back to the officers' apartment, where Aarfy has raped and murdered Michaela. When the MPs finally come they, do not arrest Aarfy and instead arrest Yossarian for going AWOL.