In the scene during Murrow's murder investigation where Mercer is looking over the parking lot fence to the ground below, he then turns and walks toward Murrow's car. At that point you see his gun and extra magazine on the same side of his body. No trained police officer, especially a detective, would have both his weapon and extra magazine on the same side of his body (unless the magazine pouch is situated in a way for the opposing hand to draw the magazine, such as in a horizontal magazine pouch) because it would take too long for him to swap the weapon into the other hand then reach around to grab his extra magazine. The proper way would be to have his magazine on the opposite side of his body than where his gun is drawn from the holster.
In a scene where Erica is sat in her apartment making a recording for her radio show, she says: "New York, like any metropolis, is an organism that changes, mutates; buildings sprout like chromosomes on the DNA of its streets". This suggests that DNA are made up of chromosomes when, in fact, chromosomes are made up of DNA.
When Erica goes into the bathroom of the bar to refresh herself, she wets her hair and head, leaving her hair dripping wet. When they cut to the next part of the scene, where she applies her lipstick, her hair is perfectly dry - no shine, no evidence of wetness - one could argue it is even styled.
The first time Erica goes to the Police Station and is asked to wait she is wearing a white T-Shirt under her hoody sweatshirt. When she walks out of the Police Station and into the Gun Shop, the white T-Shirt is now a red T-Shirt.
When Erica is interviewing Mercer she asks him if his hand was shaking when he shot someone. He then gives his reply. Later, when she is playing the tape over the air, his same reply is missing a word or two from his original taped reply.
When Detective Vitale drives to pick up the iPod kid, he passes a woman wearing jeans walking away from the park bench as he drives up; as he is getting out of his car, we see the same woman walk right by the bench.
In the scene where Detective Mercer is the bar room with his ex-wife, the amount of liquid in the detective's glass goes from full to nearly empty back to half-full multiple times throughout the sequence.
In the scene where she receives a package and before the opens the box, you can clearly see and hear something moving on the floor in the room behind her (through the glass doors). It looks like a stand for a microphone or camera being pulled out of the view.
At the scene where the two thugs were killed in the subway wagon an officer picks up a spent casing, and states that it is a 9mm and was fired from an automatic weapon. You can't tell by the casing of a cartridge what kind of gun it was fired from, and, besides that, the officer mistakes the Kahr K9 for an automatic, when it is in fact a sub-automatic.
Police say there were no eyewitnesses to a killing on the New York subway and resort to tracking down a passenger to get a possible description...even though NYC subway conductors look up and down the platform at each stop to make sure doorways are clear, which is why this train remained stopped with its doors open when one of the bodies fell out.
The goof items below may give away important plot points.
When Erica shoots the last thug, he is face up with a blood splatter pattern behind his head; however, the zoom out of the same scene shows him face down (to the left) with a blood splatter pattern to the right of his head.