It's not like they just started jailing people in 1990.
All I see is that crime was high for years, dropped drastically in the 60s, went up drastically, and is now going down again.
It's pretty hard to fit that hundred-year sine curve into any favorite theories, Left or Right. And "sociologists" aren't much help since most of them are about favorite theories, too. There are just too damn many attractive variables that fit the curves, if you're not picky about your start dates.