Stewart was a Narcotics detective who worked with Detectives Joey Quinn and Yuki Amado during their time in Narcotics.
At some point, Stewart developed a crystal meth problem and Joey figured it out. Rather than bust him for it, Joey tried to protect him from the fall he would take if anyone found out. Then one day during a bust, Stewart made a bad judgement call and shot an unarmed coke dealer. The dealer survived, but was left paralyzed. After this, Stewart went on a bender and eventually ended up committing suicide by eating his gun.
Afterward, Joey transferred to Homicide, remaining a detective. Yuki transferred to Internal Affairs and was promoted to Sergeant. She tried, but failed, to get Joey removed from the police department.