Lieutenant Kavanaugh's Investigation

Jon Kavanaugh's Investigation into the strike team revolved on squeezing Lem and Corrine into giving up Vic. It later degenerated into attempting to frame Mackey for Lem's murder

Season One 

• See Terry Crowley Murder

Season Four

Lem takes some heroin to order to obtain some leverage over a drug dealer, which he does to prevent Shane from being unjustly arrested for murder.

Later Captain Monica Rawling asks IAD to investigate the Strike Team to prove that they are innocent. IAD finds the heroin and replaces it. Lem returns the (fake) heroin to the dealer. When told that the heroin he returned is fake, he is confused but makes nothing of it.

Later Rawlings is told about the heroin, and that once of Vic's CI's, Emolia Mendez has begun spying on him for IAD. She decides that Vic is no longer her problem since she has retired. She tries to warn Vic about the investigation without actually revealing the investigation.

Season Five

Lieutenant Jon Kavanaugh approaches David Aceveda, Lem and Corrine and attempts to get each one of them to turn on Mackey.

• Corrine refused to help, even after being told about Vic's misdeeds and an affair with Danny Sofer. Eventually Vic and Dutch told her to cooperate so that she would not be made a target of the investigation. She later turned over $65,000 that Vic had given her.
• Lem refused to help until told that Vic killed Terry. He eventually agreed to wear a wire in order to get a confession from Vic. However when the confrontation between the two men occurred, Lem disabled the wire and asked Vic for the truth, warning that he would help IAD if Terry was murdered. Vic said nothing, but Lem realized the truth. However he decided to remain loyal to the team.
• Aceveda also refused but was told that he could become a target of the investigation. He decided to help in order to get IAD off his back, finally put Mackey away and make himself look good to the voters.

What followed was psychological warfare between Vic and Kavanaugh.

• Kavanaugh bugged the team's clubhouse and Vic then manipulated him into disrupting a high-profile sting, making it seem that Kavanaugh interrupting good police work.
• Mackey slept with Kavanaugh's ex-wife to make the investigation seem personal.
• Kavanaugh made a deal with Antwon Mitchell, promising that if Antwon would give him information, he [Kavanaugh] would in turn place the team where Antwon could kill them. However it seems that Kavanaugh had no intention of keeping his part of the bargain.
• Kavanaugh arrested Lemansky and then froze the team's bank accounts so that they couldn't bail them out.
• Kavanaugh forced the team to re-live the night of Terry's Murder in the hope that they would crack.
• Kavanaugh convinced Aceveda to be his double agent, pretending to give information to Mackey while actually feeding it to Kavanaugh.

Eventually Lem grew tired of the stress and decided to plead guilty and receive a year in jail, thus removing any leverage that Kavanaugh had. Kavanaugh seemed to accept his defeat even shaking Lem's hand.

However Lem decided to run rather than be killed by Antwon Mitchell in jail. This allowed Kavanaugh to restart his investigation and search for Lem. He hoped to find Lem and convince him the cooperate rather than face new charges. When it became clear that Lem would not betray the team, Kavanaugh had Aceveda convince the team that Lem had turned. Although they were skeptical, they could not ignore the possibility that he had turned. Kavanaugh hoped that the team would rush to Lem thus allowing IAD to arrest them all for aiding and harboring a fugitive. However Shane killed Lem with a grenade, removing the last hope for Kavanaugh.

Season Six

Kavanaugh became convinced that Mackey killed Lem. he began planting evidence to prove it but was discovered by Dutch and imprisoned.