Continuity mistake: Michele Riondino has just killed the snitch and is going after the witness, a Chinese woman. He holds her at gunpoint; she does not move, but in a shot she has hair in front of just her left shoulder, both shoulders in the next. (00:30:30)
Continuity mistake: Lynn Jackson collects things from the desk and looks at George Pierce, who tells her "I'll talk to him", clutching his smartphone to his chest. Next shot and his arm is down his side. (00:18:10)
Other mistake: The private investigator has a full size Glock. The Glock 21 which is a .45 ACP has the lowest magazine capacity of 13 rounds. The 9mm capacity for the Glock 17 is 17 rounds. The PI exchanges gun fire and after he fires 7 rounds, his gun runs dry. Makes no sense to bring a half empty gun to a fight, plus he just got it back from his brother-in-law. (01:05:00 - 01:06:00)
Continuity mistake: The car used in the Mayers' driveway and in which they are seen driving was a '52 - '53 Oldsmobile. Yet the "Mayers'" vehicle they wrecked and burned later in the film was a '53 - '54 Chevrolet.
Other mistake: Henry and Peter got on the school bus in the morning and Susan picked them up after school. Parents often drive their kids to/from school, even when busses are available. Busses usually aren't available for students within short walking distances to school. The day Peter looked "lost" when school let out, Christina walked him home. This indicates the school is close - close enough that Susan wouldn't need to speed to home and back during the talent show or take 45 minutes to execute the plan. (00:02:48 - 00:51:39)
Deliberate mistake: The front passenger's side mirror [driver's side is on the right] is parallel to the screen/camera yet there is a perfectly clear image of the passenger's face looking into the mirror. (00:00:38)
Factual error: Since the movie was set in the 60s, David Senak couldn't have gotten in trouble for shooting the man running away. In the 60s, the police could legally shoot any criminal running away. This didn't change until Tennessee v. Garner in 1985.