Here's Hank Voight's darkest kill on Chicago PD explained. Producer Dick Wolf started his career working on classic shows like Hill Street Blues and Miami Vice before he launched what would become a mammoth franchise with Law & Order. This series typically split episodes between the police officers investigating a given case before it switched over to the prosecution side of events. Law & Order soon became one of the most popular procedurals on television and spawned many spin-offs, including Special Victim's Unit and Organized Crime.
Wolf often has good fortune when it comes to turning TV shows into long-running franchises too, and he later proved this again with his Chicago saga. This began with Chicago Fire in 2012, which focused on a group of firefighters. Chicago Fire has run for ten seasons as of 2022 and its success led to a series of interconnected shows, including Chicago Justice and Chicago PD (which Sophia Bush left after season 4). The latter follows the police department's Intelligence Unit, led by Detective Sergeant Hank Voight (Jason Beghe, Monkey Shines).
Voight was first introduced on Chicago Fire as a corrupt, violent cop who tried to threaten Matthew Casey into dropping claims that Voight's son Justin was responsible for a car accident due to drunk driving. Voight was fleshed out much more in Chicago PD, but while he does have the respect of his unit, he's shown to be more than willing to use violent methods in the name of justice. This includes murder, and in season 3, Voight committed his darkest kill in the name of avenging his son.
In the Chicago PD season 3 finale "Start Digging," Hank Voight's son Justin is linked to the murder of a woman and is later found in the trunk of his car shot in the head. He's still alive and taken to hospital, but Voight chooses to take him off life support after Justin is declared brain dead. Voight tracks down Justin's killer Kevin Bingham and has him taken out to a remote location, forcing him to dig his own grave. Despite Sophia Bush's Erin arriving and trying to talk Voight down he is, of course, intent on vengeance. After she leaves, Voight executes Bingham and fills in the grave.
Chicago PD has never shied away from depicting Hank Voight's - who has several famous quotes - brutality, it was the personal edge to Bingham's killing that made it his darkest. Forcing him to dig his own grave and letting it sink in he wasn't going to be saved added to the cruelty, but then again, Bingham had little remorse for killing Voight's son either.