Well, was he?

* Socucius Ergalla says it's ridiculous saying Processus was a bad man and that he was nothing more than an honest tax collector,
* Thavere Verdano loved him (maybe it's not such a solid argument),
* Foryn Gilnith states he was skimming off top, and that he was corrupt, spending money on jewelery and the like. Dead Processus is wearing nothing but some Common Clothes,
* Foryn's due taxes were the highest of them all,
* If you spare Foryn, he's telling you honestly that it's the truth, and moreover gives you Thavere's ring, saying she has nothing to do with the whole thing.

No he was not :D

He was government official therefore any problems with taxes are not his fault but of his higher ups. He just does the job which has to be done as without taxes lawful society cannot function.
Furthermore, if he was skimming on taxes the issue should be brought to attention of his superiors as he was de-facto stealing from the government.

Whether he was guilty or not of any wrongdoings is impossible to answer without deeper investigation. What I am certain, his killer is guilty of murder and should be charged and arrested.