The son of a defense attorney has been murdered. 

Voight finds out that the murder weapon and bullet are connected to a case he worked 17 years ago. The man in jail for the previous murder is doing life in jail. 

Olinsky and Halstead interview the victim's parents and ask for consent to access his phone records. His father said he'll get back to them. 

Voight talks to another cop from the previous murder case about the possibility of them having the wrong guy. He tells him it's impossible, but Voight continues to investigate. He finds out a bunch of files have gone missing. 

Ruzek uses the victim's thumb to unlock his phone. 

Voight visits the daughter of the man in prison for the previous murder. She gives him a receipt for a purchase at the time of the murder. 

Voight has Platt look into Woods, the other cop he met with earlier on the previous murder.

Dowd wants Intelligence off the case. The chief agrees to delay the paperwork to buy them a little more time. 

The victim had pictures of a girl, Jo Jo, on his phone. They question her about their relationship. 

Voight talks to the previous victim's mother, who tells him she was surprised the man who killed her son was black. She saw a white guy in the store that day. 

Jo Jo admits she knows who killed Richie Dowd. She believes it is her friend Eric. Eric's father was the CI who helped put away Valentine for the previous murder. They arrest the father. 

Voight is taken to the review board for insubordination, thanks to Woods. Intelligence is taken off the case, but they keep investigating anyway. They find Eric and arrest him. He confesses. 

They offer his father a deal to admit to his murder and Eric would get involuntary manslaughter instead of murder. He takes the deal and admits that Woods framed Valentine. 

Lindsay brings the file to the review board and Woods is suspended. Valentine is released from prison.