Finding and fixing the causes of these is a much harder problem. NYC did a lot under Giuliani in Bloomberg to lower their crime in murder rate, but those have started rising again. Chicago hasn't done anything to fix their crime problem in the last 30+ years.
Dealing with gangs and mental health should be topics we are looking at.
Btw: getting rid of guns doesn't stop mass casualty events. The number one mass casualty event in the United States was done with box cutters. The number three was a van full of fertilizer. (The number 2 was a collection of many different weapons and methods)
Edit: if you want to read a good study about mass shootings in the US and their potential causes and statistics around them, check out this: https://nij.ojp.gov/topics/articles/public-mass-shootings-da...