Early in the the episode, when "Steven Kaplan" says the line "Go home, Gamer Girl", the extras to either side of him switch places when the shots reverse.
The detectives state several times that among the weapons at large was a 20-gauge shotgun. The shells in the gun safe are clearly 12-gauge and the shotgun seen near the end is also 12-gauge.
Benson incorrectly explains the effects of New York's "Son of Sam" law to Leslie, stating that he could lose the profits from his "Glasgowman" video game as proceeds of a criminal act. New York's law applies only to the perpetrators of the crime. However, it is likely that Benson was deliberately lying to elicit Leslie's cooperation with the investigation.