The long term trend is simple demographics. The baby boomers are getting old, and most violent crimes are committed in youth. Crime trends have always followed the demographics of boomers.
Crime way down in most those areas too.
....yes, demographics do play a role, but so has the internet and redevelopment.
Most of the young are too interested in playing games on their x-box, their computer and their i-phones to do the hard work of crime, even if their families were involved in it. The obesity epidemic has had its effect as well on the criminally inclined. It’s much easier to do business over the internet and by mail than it is to do turf wars and corner drug drops like they did in the 90s.
Redevelopment in downtown and the rest of the county has also had a really positive effect from what I can see. LA really has got the laid back image, even in the criminal class. Do your business over the ‘net and you are much less likely to get hassled by the cops, or get shot at by rival gang members.
CA’s three strikes law keeps a lot of career criminals in prison. One of the few good laws we have.
I submit that another factor is illegal aliens are not arriving in as large numbers, since work for them is less available. It may be that new arrivals are more susceptible to being manipulated into committing crimes.