It definately is lack of prosecution . . .
Take St Louis for instance. At a Conference on gun crime for police chiefs St Louis' Chief said:
"One thing we have to be aware of to give context to this whole problem is that we are looking at an urban problem. It’s much less a suburban or rural problem. It really affects young minorities— Hispanic and black males. I think that the suspects devalue life, the victims devalue life, and the system also devalues life. When you look at the shooting victims and suspects in these neighborhoods, you see 20 or 30 felony arrests, with eight convictions.
Often the convictions don’t result in any jail time at all; they’re getting probation on top of probation. This has caused a lot of us in cities to move toward federal prosecution, because we know on the state level it’s a hit-and-miss prospect: they’re arrested, they’re convicted, and they come out multiple times.
In Missouri, there’s a type of probation people can receive, and it has made it very difficult for us to establish a person as a convicted felon. I’ve heard other chiefs talking about the fact that a weapons charge in their state is only a misdemeanor offense. But in St. Louis, a weapons violation can turn out to be no offense at all. An individual will get arrested for a weapons charge, which is a felony, and often they plead to that case and get an SIS—a suspended imposition of sentence. It means that if you serve out your probation, which everybody does, that conviction is erased.
So if you’re arrested again with another weapon, you don’t have a conviction on your record, so you’re not a felon in possession of a weapon. If you continue to get multiple SISs, you never become a convicted felon. These offenders will often show up for other crimes, and if they never have a conviction, then you’re never able to put stiffer charges on them."
And not only are these hardened offenders back out on the street, they never become prohibited persons as far as gun rights disability goes . . . A person who has been arrested multiple times for gun crimes can go into a gun store and pass the NICS check . . .
I don't disagree that leftist social policies nurture criminality but liberal hug-a-thug justice systems where clearance rates are more important than protecting the public keep violent criminals on the street and definitely increase crime, especially gun crime including murder. My suggestions remove that discretion from local prosecutors and judges.