Factual error: While using the phone in his cell, Dr. Lecktor asks an operator to dial a Maryland area code, but is then connected to the University of Chicago. (00:30:10)
Factual error: Dr. Lecktor's cell has the hinges on the inside of the cell. They should be on the outside so Lecktor can't compromise them.
Factual error: When Reba is in the darkroom with Dollarhyde she mentions that he speaks very well but avoids fricatives and sibilants. In linguistics sibilants are a form of fricative and Reba would have known that since she'd obviously studied linguistics. The writers likely meant that he just avoids sibilants (to avoid sounding homosexual) but wanted it to sound more technical. Sibilants in English are the 's' in "see", 'sh' in "shout", 'z' in "zoo", and the 's' in "pleasure". Fricatives would include sibilants as well as the 'f' in "fine", 'v' in "vine", 'th' in "that", and 'th' in "thing" (01:17:30)
Chosen answer: He figured out earlier that the Tooth Fairy drives a van. Graham noticed that at one of the houses, the Tooth Fairy knew everything he had to do and bring with him and at the other house, he didn't know about the new lock on the door. He concludes that this is because the Tooth Fairy got his information from the same home movies that Graham was watching. Once the films were traced to the lab where Dolarhyde worked, it was easy to link them back to him as the only person who'd had access to both families' videos and also drove a van.
Captain Defenestrator