Race aside, or in conjunction with, if you want less violent crime and murder: also reduce your fertility rate
The homicide increase from the mid-1960s onwards was at least in part driven by the baby boomers coming of age 20 yrs or so later, and young men do a lot of murdering relatively speaking. Throw in a crack cocaine epidemic in the 80s/early 90s and other possible factors (e.g. lead,internal migration to the cities) and up it went.
And then....just declined, not just in the USA but other western nations as well (so not race, or govt policy, related even though this can have an exponential effect)-older people just don't have that killer instinct to the same degree

Homicide victimization rates, 1900–2013
