Aside from a couple of dysfunctional police departments, everyone wants to catch violent criminals and put them away—no one is arguing against that. The problem is that they can’t be found for a multitude of reasons, this is also compounded by how easy it is to acquire bullets and firearms in the US.

I think California tried to tackle this issue by fingerprinting bullets (microscopic stamps I think) which can then be traced back to the person who bought them, but these people just end up buying bullets from other states and transporting them to California.

This is a very complex issue, prosecutors can’t just wave a magic wand and selectively put these people away. You have to find them, and build a case against them that has proof beyond a reasonable doubt that they were the perpetrator(s).