Factual error: FBI only deals with federal crimes. They would not be involved in minor drug offenses.
What They Saw in Southie High - S1-E2
Other mistake: Agent Rohr asks who the cold case is related to. A dossier is given to him and the front cover contains a photograph and the name "Kanicki, K". Agent Rohr says "Kelly Kanicki" but there was no indication of the full name, just the initial. (00:08:30 - 00:09:00)
The Deaf Sage of Pompeii - S1-E9
Factual error: This show takes place in 1992. The officer sitting down has a Glock generation 3 handgun with the finger grooves on the frame in her holster. This is the third generation of Glock, which wasn't available until 1998. (00:51:50)
Factual error: Throughout season 2 there are a few shots taken of buildings with PTZ style surveillance cameras attached to said buildings. PTZ cameras are the ones with an arm and a ball with a black lens spanning 360°. This show takes place in 1992, and from what limited dates as to surveillance camera creation I could find, PTZ cameras were not available until the 2000's. In 1992 the large blocky ones were only available with terrible resolution.
Is the Total Black, Being Spoken - S2-E3
Plot hole: Jimmy was willing to give Cathy $10k in cash for her troubles and to help her out. She wanted to sell drugs instead of getting his charity. Now he's having a problem fronting her the same amount of money worth of drugs. He's saying his dealer will hurt him if he doesn't pay him back. Makes no sense how he had $10k to give her and now he needs her to pay back the $10k front of product he gave her. What happened to his $10k worth of charity? Why can't he use that to pay it off? (00:42:04 - 00:43:25)