Continuity mistake: During the street scenes it appears to be fall with leaves on the ground, grass green and streets and sidewalks dry. However, when police raid the park worker's house there is snow on the house roof and on the ground. When the police stake out the same house, there is no snow on the house roof or ground. (00:36:00 - 00:41:00)
Character mistake: When Ruzek and Voight are questioning Wade Henslow (the father of missing girl) at the station, after finding out he lied and set up his own security to find his daughter Adam looks at Wade Henson but addresses him as "Mr. Larson" which is actually the last name of one of the kidnappers they found DOA who got into the gun fight with his security guy, the ex-cop Kenny. (00:21:26)
Character mistake: Before Kevin Atwater and Doyle fight they both put their badges and guns down on a barrel. After Atwater beats up Doyle, he retrieves Doyle's gun and holds it to Doyle's head and drops it to the ground. Atwater walks away, but he never retrieved his own badge and gun before walking away. The gun and badge are on the barrel, and he does not return to retrieve them. (00:58:37 - 00:59:32)
Factual error: The cops raid a house and find some rifle ammunition. The female cop says "cop killers." A few seconds later three cops are looking at the bullet and a box used to store it, it appears to be a 5.56x45mm round used in the AR-15 style rifles. All high powered rifle ammunition, doesn't matter if its bullet is fmj or armor piercing will go through soft armor which is what all police officers wear. Such ammo is available to civilians in every store. All rifle ammo could be considered "cop killer." (00:03:50 - 00:04:56)
Continuity mistake: Toward the end of the show Voight and Ruzek are in their car chasing the suspect who is running. Sgt. Voight gets out of the vehicle first and is chasing the suspect toward the stairs only a few yards away. When they get to the stairs Ruzek is in the lead.
Continuity mistake: Atwater and Rojas begin to chase a suspect out of the library where he had been spotted by a uniformed officer. As the chase begins Atwater moves ahead of Rojas with the officer in a distant third place. As they emerge from the rear door Rojas exits first, followed by the officer with Atwater behind him by several seconds.
Continuity mistake: Officer Jay Halstead shoots a suspect and jumps in to render first-aid. As he goes to render aid he tosses his police handheld radio. Shortly after, his partner calls him on the radio - he answers the call immediately and the radio is in his hand. He doesn't appear to reach for it and if he was rendering aid to gunshot victim he would need both hands. (00:19:00)