It appears though that he has been offered some sort of plea deal. If he agrees to it, he'll most likely receive a reduced sentence covered by time already served, and not have to register as a sex offender.
Why doesn't Perdue just pardon him?
Because (1) what he did was illegal then, and (2) because what he did seems to still be illegal now (albeit with a different punishment). Pardoning is clearly not the correct legal course, though I do believe he should have been let out of jail a long, long, long time ago.
A high school senior having sex with a high school sophmore shouldn't result in a ten-year jail sentence.
