Despite what people think, AI isn't about any kind of "liberal agenda", they're just about wrongful imprisonment, torture, and basic human rights.
That'll get you started in statistics, and then you can start looking for the various Dept. of Correction websites in each state to see what initiatives they have, and you might even be able to get at their stats (although usually you have to ask or FOIA to get them).
"Human rights" is a liberal concept! Paine and Mill were liberals. Without liberalism, the idea of human rights never would have existed. Indeed, you can almost define liberalism as that political philosophy which exalts human rights as the highest good.
The Bureau of Justice collects statistics annually thanks to the Prison Rape Elimination Act. Here's a link to a relatively recent study based off of a survey of over 80,000 inmates:
