Factual error: Dominic Wingrave says "it took me 6 years to do the math." Not something any British person would say - in the UK it's always "maths."
Factual error: The FBI agents are searching a house with their weapons drawn. Each agent is going through the house with their fingers on the trigger. At one point, one agent has her finger on the trigger while her partner is in front of her as they go down some stairs. The correct officer safety practice is to have your trigger finger off the trigger and along the slide of the weapon until you are engaging a suspect and need to fire your weapon. (00:30:39 - 00:31:09)
Factual error: The show, which is set in California in 1947, mentions the gas chamber, lethal injection and the electric chair as methods of execution in the state. Two murderers are sentenced to death by lethal injection and one is depicted being instead executed in the electric chair, which the governor states has been brought out of retirement for the occasion. In fact, California adopted the gas chamber as its sole method of execution in 1937 (having previously used hanging). Lethal injection was not used in the United States at all until 1982 and not adopted in California until 1993 (becoming the prime method in 1996). California has never used the electric chair.
Factual error: In Massachusetts, Atticus, Leti and George are attacked by the local sheriff and his deputies, who are patrolling the county roads. In Massachusetts, sheriffs run the county jails, but they do not (and did not) handle routine policing, which is the responsibility only of municipal police departments.
Factual error: A man enters a bank and begins firing his Glock 9mm pistol. A few of the men he shoots, jump up in the air after the rounds impact their bodies. Bullets hitting a body will never make it jump, or fly in the air. (00:00:01 - 00:01:46)