"Nope! I know who I know... and who I don't know. And I DON'T know her." - Zuben, after being questioned about Lucy
Military Service and Family
Zuben was part of an all-replicant Off-world combat unit called Lightning Squad that fought in the Battle of the Gemini prior to his involvement in the Moonbus hijacking. His involvement with the renegade replicants and/or humans is somewhat known; Lucy calls him Uncle Zuben, and he is part of a crime committed as a response to Runciter's implied molestation of Lucy while she worked there.
He, along with Clovis, were responsible for the animal murder at Runciter's, murdering animals real and fake with a butcher knife. It is this crime that kicks off a full-scale police investigation and ultimately Ray McCoy's involvement.
Events of 2019
Ray McCoy's investigation
McCoy's investigation at Runciter's reveals clues that indicate there was a large, hobbling suspect as well as one whose stride was very particular (Zuben and Clovis, respectively). Other clues found near Lucy's desk reveals a Howie Lee's receipt, prompting McCoy to take his investigation to Chinatown.
When Ray McCoy arrives at Howie Lee's, Lee tells him that Zuben is a new chef that has only worked for him for a couple of months. McCoy goes out back to interrogate Zuben about Lucy, and the latter ends up attempting to escape. Before he flees, he dumps soup on McCoy in an attempt to slow him down.
(McCoy can either dodge the soup by clicking quickly to the right before Zuben is able to finish, or fail to react in time and get slowed down as Zuben makes his escape.)
Retirement or Escape
McCoy chases after Zuben, making his way through the back alley and into an abandoned warehouse, finally reaching a hallway with a locked door. Zuben, if he ran and McCoy was not fast enough, or refuses to chase him altogether, will not be here. If McCoy was quick enough, Zuben will jump down from the ceiling and approach McCoy with a butcher knife. At this point, McCoy has the choice to shoot and retire Zuben or put his gun away and let Zuben go.
Alternatively, if not chased down in the back alleys, McCoy will be ambushed by Zuben the next time he returns to his apartment. The same choice is offered here: shoot Zuben or let him go.
If shot at either location, you can pick up his war photo from his corpse.