Factual error: After Ressler tells McChesney he wouldn't be surprised if one day she's tracking down sequence killers, McChesney replies, "Not sequence killers. Serial killers. That's what they should be called." But it was Ressler who claimed he coined and is often credited with coining the term "serial killers" (at least in the U.S). ** After showing pictures of some of Bundy's victims, Ressler is shown and it is pointed out, "He [Ressler] is credited with coining the term 'serial killer'." (1:31:30). (00:26:40)
Factual error: Unless left in the vehicle (not the case here), towed impounded vehicles do not have keys. Moreover, lacking keys, a valid registration, possibly proof of insurance, and new plates, vehicles bought at a NYPD auction are to be TOWED away. A newly-purchased auctioned vehicle, such as the Navigator in the movie, is "ticket-" or "citation-ready", not ready to be driven on the streets.
Other mistake: Blood gushed out of the bound man's lower inner arms that were slit with a knife from below the elbow to the wrist (then turned toward the ground). A switch to an aerial view showed no additional blood dripping (while he was still alive). Also, blood would not pour out of his arms to the ground in a horizontal stream like it did. (00:02:04 - 00:02:27)
Continuity mistake: When Hagmaier is in the Florida State Prison room waiting for Bundy, his hair changes. Initially, his short bangs are straight across the middle of his forehead. When Bundy sits down, Hagmaier's bangs and top of head are "fluffier" (perhaps blown dry) and combed to the side. (00:11:05)
Other mistake: The issued sidearm for the Spanish National Police is the H&K USP 9mm Compact, which has a capacity of 13+1 bullets, and the Civil Guards' is the Beretta 92fs/M9, which is a 9mm and has a magazine capacity of 15+1 bullets. As of 2020 the Beretta is being phased out for the H&K USP C. The police officer fires a total of 5 bullets from his Beretta then the slide locks back because its dry. He has no magazines for reloads either. I highly doubt the Spanish police issues 5 bullets to their officers. (00:33:00 - 00:35:30)
Continuity mistake: Helen's slipper is at about a 45° angle toward the right of the screen when Miss Willoughby finds it. When Detective Jimmy shines his flashlight on the slipper, it is facing the opposite direction. The second time Jimmy shines the flashlight, the slipper is at a steeper angle. (01:00:33)
Revealing mistake: During one of the chase scenes, an SUV hits a rock barrier and flips over landing on its top. The car spins around, and we see that it is empty. The driver then climbs out as if he was just in the vehicle.
Plot hole: Diabolik blinks in Morse code to his accomplice the location of one of his hidden stashes. He says it's in 'the third brick to the left' and the street name, but no address or other reference. She (who previously knew nothing about the location) finds it immediately. It's worth noting that the movie is a faithful adaptation of a couple issues of the comic, but this bit of subplot is a fresh addition and the original hiding spot in the 1963 issue was a plausible one (cave behind a specific waterfall).
Character mistake: After banker Karl was reported missing from his home, the police detective did not even think to locate his car - which he could have merely driven away in (meaning he was not kidnapped).
Continuity mistake: The height of the stack of magazines on the coffee table in front of John changes with the camera's view. Front views of John show a high stack of maybe 15 magazines. Side views of John show a much shorter stack of several magazines. (00:25:03 - 00:26:07)