Can you imagine the resources that would be necessary to conduct a real investigation of that many homicides? I would venture to guess that most convictions are cases where the perp was standing over the dead body with a smoking gun, and most of those pled guilty with no trial.
It is a feedback loop. You overwhelm the system. They system breaks down, and more bad stuff happens.
Obama and Rahm really kicked this off with the “Ferguson Effect”.
It takes a lot of work to put the genie back in the bottle.
---everyone (especially the cops) realized that the next homicide was usually part of the solution of the preceding one---