A cop is murdered and suspicion falls on someone who has been holding a grudge against the officer.
Intelligence works hard to solve the case but Dep.
Supt. Samantha Miller is hesitant to defend him until she knows the whole story.
Air Date: Wednesday, January 27 (10-11 p.m. ET) on NBC.
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CHICAGO P.D. -- "Unforgiven" Episode 804 -- Pictured: (l-r) Tracy Spiridakos as Hailey Upton, Jesse Lee Soffer as Jay Halstead, Jason Beghe as Hank Voight, Marina Squerciati as Kim Burgess, Patrick John Flueger as Adam Ruzek, LaRoyce Hawkins as Kevin Atwater -- (Photo by: Matt Dinerstein/NBC)