Background
From its youngest age, Dzaalih Flain was not a typical Kallidahin. He was an inquisitive child, but, unlike other Polis Massan, he felt like asking questions was a much better way to get answers than digging through rocks. There were people who knew what you wanted to learn, who knew that you wanted to learn what they knew and who would not tell you anyway. So much information was hidden that way that Dzaalih felt frustrated at the kind and compassionate ways of the Kallidahin.
He would probably have lived all his life in such frustration if he had not joined the "police force" in Kallidah, a small outfit considering the social structure, mostly dedicated to investigating off-worlders that swindle unsuspecting and trusting Kallidahins. There he found its calling, filling the minds of suspects with dread and getting confessions out of them. For a time, while the rest of the force was wary of its methods, he was their best interrogator.
And then came the "incident". Sure Dzaalih might have gone a bit far on that swarmy Neimoidian that pretended that the shares it had sold were shares of a perfectly legitimate trading company with exclusive rights for importing Core Worlds technology into Kallidah. But they knew it was false, and he kept trying to convince them. And so Dzaalih pushed him again and again, going further and further into his mind, until its weak Neimoidian mind snapped and it went catatonic.
Dzaalih failed to see what the big problem was. He was guilty. Good riddance, to be honest. But there was an investigation, he was kicked from the police, and he felt unfit for most other jobs. So he went off-world, offering its interrogation services to various outfits, never staying long in any position, until he ended up in Nar Shaddaa, with an opportunity to work for the Carbon-Scores syndicate.
Motivation
Expertise (Interrogation/Psychology): Dzaalih has a very specific set of skills that he wants to use and enhance so that he gains the knowledge that comes from breaking minds.