OP, I don't know how you ended up on DT (other than it's a rotating system now), but if you think this guy is still the shady person who tried to blackmail and impersonate you, don't hesitate to leave him a negative. That's what the power of being on DT is all about.
However, if you think he's being sincere then let the neutral stand--but in my cynical head, he might be trying to make peace with you
precisely because you're on DT now, and any neg left for him has a much greater impact.
I also reviewed a lot of other feedbacks I sent over years and changed most of them to the neutral.
Good, I'm glad you're being responsible--but again, if someone deserves a negative, leave them a negative.