“...plea for help on Thursday and her murder on Sunday.”
The cops had open warrants for domestic violence. The perp had an active moniter. The victim called for help and was ignored, then murdered.
You a cop? You have cops in your family? Why are you trying to deflect obvious failure of duty?
And if they had arrested him again likely Judge "Risk Other People" would have let him out again.
The police arrested him and brought him in. That is all they can do.
Take a deep breath and look at the situation rationally.