In the opening sequence, when the shooting takes place, the train is an A train. After the credits, when the police board to investigate, it is a C train.
E.A.D.A. Ben Stone tells Captain Don Cragen to arrest Laura Biasi for second degree murder. Yet when Sergeant Max Greevey is advising her of her rights and explaining how arraignment works he tells her she's been charged with negligent homicide. Murder in the second degree and criminally negligent homicide are two very different crimes, with very different sentences. Murder in the second degree is when someone with malice aforethought, intentionally causes the death of another person, it is a class A-1 felony with a minimum sentence of 15 years to life. Criminally negligent homicide involves causing someone's death by acting in a manner that was reckless, inattentive, or careless. In addition if you recklessly fail to act and as a result someone dies (an example being if you are a life guard and see someone drowning and you fail to help them and they die), you could also be found to have committed criminally negligent homicide. Criminally negligent homicide is a class E felony with a sentence of 1-4 years.
In the opening shots, all the trains are scruffy and have corrugated sides below the windows; however, when the train is coming into the station after the shooting, it is shiny new and smooth-sided.
The dates shown are in the middle of February. On the wall of the hospital administrator's office when the detectives are talking to him, the calendar shows March 1999.
When the detective picks up the shell casing from the blood on the train floor it is shown as a rimmed handgun cartridge. The type used in revolvers. Which would not have been left behind at the crime scene unless the shooter took the time to open the gun and remove the spent shell.
The train announcement states that the next stop is 23rd street. The A train is express and bypasses 23rd street except during late night service.
As the detective go down the steps to the 23rd St-8th Ave subway station to investigate the shooting, the sign shows this station as a stop for the A, C, E, N,Q, R, 1, 2, 3, 7 and 9. Only the C and E stop at this station. The A runs express on this line. The N, Q and R run on the BMT Broadway line. The 1, 2, 3 (and 9 at the time of the episode) run on the IRT 7th Ave line. The 7 runs on the IRT Flushing line.
When Detectives Max Greevey and Mike Logan are talking to Captain Don Cragen in his office the first time, there is a man on the other side of the window, pouring coffee. But there is no coffee. The pot is empty.
When discussing the case with D.A. Adam Schiff, Ben Stone first calls him "Ed" and then responding to Adam's reply, calls him "Paul" (the name of Ben's assistant who is not in the scene).