The conviction of a 17-year-old case is challenged when a weapon linked to the crime is recovered in the upcoming episode of "Chicago P.D." season 4.

Titled "Grasping for Salvation," next week's episode will see the team find an unsettling connection between two murder cases. According to the official synopsis, the officers are investigating the murder of a teenage boy when Voight (Jason Beghe) makes a surprising discovery: the murder weapon is connected to a case that he oversaw almost two decades ago.

The slain victim's father (guest star Philip Casnoff) is a prominent defense attorney, and he tries to make Area Central Homicide take over the case instead. While the investigation is ongoing, Voight tries to find leads on his own and decides to look into the old case. He teams up with his former partner, Lieutenant Denny Woods (guest star Mykelti Williamson), to see if they actually sent the right suspect in jail.

Meanwhile, Burgess (Marina Squerciati) continues to be out of the picture after she took a leave of absence from the unit. The character had to take a break because of Squerciati's real-life pregnancy. In a recent interview with TV Line, the actress said fans should not expect much development on the blossoming relationship between Ruzek (Patrick John Flueger) and Burgess since her character is away.

"I don't think the Ruzek relationship is really ready to blossom quite yet," Squerciati revealed, adding, "They're still figuring each other out and figuring out how to work together."

The actress went on to say that with Burgess' new role as guardian for her niece and sister, finding time for love will not be a part of her priorities. "I don't think she's really thinking about relationships at all right now, unfortunately," Squerciati continued.

The fourth season of "Chicago P.D." airs every Wednesday night at 10 p.m. EDT on NBC.