It's really not worth to talk much about Tzsk's youth. For like many children stuck in the dank slums of Maro Tszk did what he could to survive. Learning how to steal, mug, and grift for his bread and butter early on in life it wasn't much a transition for the adult Tzsk to move into a small gang of so called "organ harvesters" criminals specialized in the removal of cybernetic limbs and organic grifts to be sold on the black market to deep desert gangs and underground gladiator rings.
He worked with four other gang members to find marks with profitable augments. The job was relatively simple even if each part was fairly complicated. The mark, typically referred to as the "lamb" or "sheep" would be led to a specially prepared location, often a hotel room, though an abandoned building or back alley could do in a pinch. The lamb would typically be drugged, or otherwise heavily inebriated a job left to one of the more convincing and seductive members of the crew. Once the lamb was brought to the location they would quickly be rendered unconscious and the lamb would be "sheared" by the gangs group of amateur surgeons removing any profitable augmentations.
Tszk's role in this was that of "shepherd" if the target was getting rowdy, if the cops or a rival gang were too close or getting savvy, if the target's friends were starting to catch on, if he had even the faintest itch in his antennae he would step in and either abort the job or fix the problem himself.
For a while, life was decent, the money they earned meant he didn't have to live in a trash can. The respect their reputation gave them meant most rival gangs stayed away from them. The fact that they didn't kill their lambs and went out of their way to ensure their targets survived meant the cops were far easier to bribe as they didn't have to clean up after a murder.
That all changed when the shearer decided to take out a lambs artificial heart.
It proved a turning point for Tszk. He himself had never taken a life, maimed, stole, battered, all necessary things when it came to the grim algebra of survival. Yet his part in it basically meant he was every bit as responsible as if he had torn it from the ribcage himself.
When he brought his grievances to the gang's leader they argued. Shots were fired, and fearing for his life Tzsk grabbed all the credits he had been saving up and grabbed the next flight off the planet. Ever since he has been on the run trying to find any kind of redemption for actions in the past. The starfinders offer him an opportunity to find that redemption and keep a life on the move the better evade authorities, his old gang, or past victims who might recognize the faintly metallic form of Tszk.