Although they are not the only source of bounties, as far as the majority of the galaxy is concerned, the Empire is the only legitimate employer for those who capture fugitives for pay. As the sole guarantor of galactic “law and order”, the Empire does not allow individual planetary governments any jurisdiction whatsoever beyond their own star system – their only recourse when a wanted criminal flees to another world is to pass it along to the Imperial military. The Imperial Army and Navy, which control the spacelanes in a state of permanent martial law, enforces their laws directly (with some assistance from paramilitary bureaucracies like Imperial Customs, or armed civilian groups with nebulous authority such as COMPNOR). However, the Imperials are well aware that their military machine, meant for hunting down dissident movements and pirate fleets, was ill-suited for tracking down lone individuals and solitary freighters. Therefore, they allow aggrieved planetary governments to post bounties on wanted ‘criminals’.
There is no “due process” for a planetary government or moff who wants to place a bounty; the only question is whether the proposed target has any value to the Galactic Empire and the reigning Grand Moff. Aside from that, questions of guilt or innocence are unimportant, and the bounty is posted. The higher echelons of the Imperial military, as well as the Emperor’s personal Guard, also arrange for bounties to be posted on enemies of the state; these tend to be an order of magnitude larger than other bounties. As a result, the top 10 bounties are all for Rebel Alliance political leadership. However, even the most amoral bounty hunters have been hesitant to go after the likes of Mon Mothma or Borsk Fey’lya, since the risks would be nigh-suicidal and rebel retaliation would be certain. Interestingly, the so-called “Heroes of Yavin” spoken of by Rebel-sympathizing worlds – Princess Leia Organa and a mysterious force-wielding pilot – have not appeared as official bounties yet. Apparently, the officers in Lord Vader’s handpicked military force, “Death Squadron”, are firmly opposed to bringing in independent operators in the hunt for Leia, her pilot, and her smuggler contact, wanting all the glory of avenging the Death Star for themselves.
The rules of bounty hunting (Imperial or otherwise) are complex, nuanced, and sometimes arcane. Indeed, for centuries now, it has been common practice for successful bounty hunters to keep lawyers and legal scribes on retainer. This is of particular interest in the case of the lost Sa Nalaaor which the recently-recovered hyperspace pod points to; many of the Separatist leaders believed to be aboard that ship had bounties assigned to them in the early days of the Empire. Since it has been almost 20 years, those fugitives have been presumed dead, and so the bounties on all of them have been reduced… but not eliminated.
The upshot of this, combined with an interesting quirk of the “dead or alive” status of these bounties, is that licensed hunters pursuing the Sa Nalaaor have the chance to do a little of what might be called “bounty archaeology”, or (less charitably) “bounty graverobbing”. If there is a bounty on a given fugitive ‘dead or alive’, then even a dry skeleton pulled out of some old wreckage can be worth thousands of credits if the DNA scan checks out or they have identifying documents with them. There is no limitation on how long the mark has been dead; the only rule is that the head and torso (or equivalent) must be accounted for. (remember, this is a universe where your severed head or disembodied brain can be kept alive for a time; there is actually an item in the book I own, Dangerous Covenants, that can effectively reverse death and stabilize someone as long as their brain is mostly intact!)