How do we deal with them now? Is dealing with serial killers the day to day of the police? Is that their primary function? Do they even really do anything about it without constant prompting from victims and the community?
I've been a victim of physical and sexual violence. Nearly every woman I know has been at some point. None of us have ever had any positive experience with the police. At most they hand wave us away, at worst we are accused of being liars and of wasting their time. Police don't prevent anything. They don't solve anything. They don't address anything. They are only occasionally turned towards a specific person who has done something wrong and used a means of state violence against that person. That is an exceptionally rare occurrence. They are the perpetrators of violence many times more than they are the defenders of victims.
Essentially, what is being currently done about the john Wayne Gaceys of the world? What is currently being done about the Bill Cosby's, about rapists and pedophiles? What are the police currently doing that actually prevents those things from happening? Nothing. They only do anything after something has already happened. And they don't do anything to prevent those things happening again. Their daily job has literally nothing to do with the John Wayne Gaceys of the world. It is in the things I listed in another comment. In rent enforcement and eviction, in enforcing private property and means of production, in collecting menial tax from the impoverished, in defending the interests of the rich and of the state, and in harassing minorities while enforcing hierarchies of gender race and class.