Possibly your pick out of Know: Geography, local, Arcane or Religion. He gets around, and with a rapsheet that includes two planeicides, you've heard of him on the news. Of course, all you have to go on is his name.
Also, every single one of you knows that Habenalter is basically a prison demiplane that no one possibly has or CAN escape from, but you're not privy to specifics.
Phaedrus, if you'd like, Kyx can be an ex-inmate.