Hank Voight's (Jason Beghe) personal tragedy will lure him back to his dark side when "Chicago P.D." returns for season 4.

At the end of season 3, Voight's only son Justin (John Segarra) was killed by a gunshot wound. This will reportedly turn the head of Chicago P.D.'s Intelligence Unit into a vengeful man who will not stop until he finds out who is responsible for killing his son.

Speaking with The Hollywood Reporter, showrunner Matt Olmstead revealed that Justin's death will definitely bring back the ruthless Voight who first appeared when the character was introduced in the third episode of "Chicago Fire."

"We have a Voight that is hell-bent," Olmstead said. "[He's] a guy who is completely blinded and will do anything legal, illegal. If I have to pay money, I will. If I have to pull a gun, I will. He's cautioned by people upstairs and he says, 'You'll have to put a bullet in my head to stop me.' He's just going 100 miles an hour looking for who did this to his son, which affects everyone."

But Voight will not be the only one who will be affected by fury over Justin's death. According to the showrunner, Erin Lindsay (Sophia Bush) will also feel bad for the loss, especially since she practically grew up with him. Voight took care of her when she was a troubled teenager.

But she will be more concerned about Voight's welfare, since she knows what he is capable of.

"[She] is trying to prevent Voight from doing anything that is going to get him fired or killed or otherwise," Olmstead stated.

However, Lindsay will also explore a new phase in her relationship with Jay Halstead (Jesse Lee Soffer) in the upcoming season as they finally got Voight's blessings to date each other despite working for the same team.

"We want to have them move in together and just play the baby steps of what it's like to live with someone [for] two very independent people who have always done their own thing," Olmstead told TVLine in a separate interview.

The fourth season of "Chicago P.D." returns to NBC this fall.