The family did ask the police to investigate her, but the LAPD under then Chief Daryl Gates would not do it even though Officer Lazarus had threatened the victim a few months earlier.
That question is screaming to be answered as you read the story in the original post. No explanation was given for the non-investigation but it's obvious that whoever was in charge of investigating simply didn't want to go there if it led in the direction of a fellow police officer.
Shameful.