My access to the Planescape books is limited, given that I don't physically possess any, and I have failed at weilding the considerable powers of the internet to provide myself with a satisfying answer. So, I come to you for aid!
As far as I understand, petitioners are the souls of the dead that, uh, re...form? Recreate? Reappear? Travel to? a certain outer plane depending on the soul's alignment during life. Most of them forget about their past lives and they have different forms according to which plane they pop at - larvae in the Lower Planes, uh, lantern archons in the Upper ones, I can't quite remember.
Now, we have the Dustmen who believe we're all already dead and stuff, until we die and pass on to True Death. How does this apply to petitioners? Are they still stuck in some kinda false death, still unable to let go? And how does it apply to undead - not the ambling mindless skeleton types, but for instance, a ghost who can't rest peacefully until his killer or whatever is brought to justice?
Thanks in advance!
Dustmen believe the petitioners are in another stage of death. All petitioners strive for improvement, to advance into other outsider forms or merge with the plane/power, for the Dustmen that is a false path, clinging to anything. The same is with the intelligent undead, vampires or ghosts are still affected by their former lives, not accepting they're dead.