On Chicago PD Season 5 Episode 4, Intelligence is working an undercover assignment that's thwarted when Ruzek got made by the guys they were trying to bust. 

Eddy, who was working with Ruzek and unaware that he was a cop, ends up dead. 

Even though they technically know who the killer is, they can't do much without concrete evidence. 

The investigation is hindered by the "no snitch" culture on the city's south side. Folks know that if they say anything, they'll end up dead too. Even on his deathbed, Eddy refused to go out like a "snitch."

Ruzek blames himself for the death and gets into an altercation with the suspect, which gives Internal Affairs a reason to launch an investigation against him.

Voight always takes care of his own and tells Ruzek that the official story is that Andre Walker overpowered him and he had to defend himself and his partner. 

His partner, Upton, knows the truth and she's a "by the books" cop. 

But she come through, telling the witness to retract her statement.

Denny assumes that Voight once again erased a case in favor of one of his own. 

Voight becomes suspicious of Antonio, who lied about parent-teacher conferences to meet up with States Attorney Nathan Potter, a rising star whose done a lot of work with Denny. 

Atwater also has a personal connection to the case.

His 15-year-old brother was a witness to the shooting of Eddy's brother, Roland, in a convenience store. 

With the "no snitch" policy, he's hesitant to speak up but eventually ID's the suspect. 

But just because the killer is behind bars, doesn't mean he's safe.

Atwater is paranoid, trying to keep his brother safe because he has a target on his back.