Top left: Graham is at a standstill in trying to figure out how the Tooth Fairy selects his victims. Top right: He and Crawford have an argument. Above left: The argument gets Will wound up, and then he has an important insight: the Jacobis' home movies show that a door in their house uses a padlock (click image to enlarge). This leads Will to gradually realize that the killer has seen these same home movies. Above right: Crawford looks over at Will in amazement at Will's ability to experience flashes of deep insight.
Let us discuss the Graham 'revelation' scene. Graham is viewing the victim families' home videos once again in a final attempt to find out how the Tooth Fairy selects his victims, before the killer strikes again (there is only a very short amount of time remaining until the next full moon occurs; the Tooth Fairy has been operating on a lunar cycle). Graham tells Crawford that the killer dreams about being wanted and desired, so he changes people into beings who want and desire him. Will mentions that Lecktor had told him that "If one does what God does enough times, one will become as God is." Graham then says to Crawford, "You put it together, you get: If our boy imitates being wanted and desired enough times, he believes he will become one who is wanted and desired and accepted. It'll all come true."
Graham tells Crawford that the Tooth Fairy did not pick his victims randomly: "Jack, all the women have a bloom on them. He didn't win them in a lottery - he picked these women! There's selection and design in his choices."
Next, after having a heated argument with Crawford, Will goes back to watching the Jacobi home movies, and he spots padlock fixtures on a door in the family's house. Will then realizes that since the Tooth Fairy had brought a bolt cutter with him on the night he murdered the Jacobis, he had expected there to be a padlock on the door, whereas there was a deadbolt on the same door on the night of the murders. A few moments later, after looking over some case papers, Graham switches to watching the Leeds home movies, and realizes the killer knew to bring a glass cutter to break into the Leeds house on the night of the murders, even though he couldn't have seen the glass in the Leeds' kitchen door from the street, while casing out the house prior to the murders, because the Leeds' house had a tall fence that would have blocked Dollarhyde's view of the glass. Will makes a quick phone call to the FBI, then he goes back to watching the home movies again, and gradually has a series of realizations that the Tooth Fairy has seen the very home movies that he (Will) is currently watching. A few moments later, while Crawford is on the phone relaying information about the home movie film can labels to Will (the cans have been kept in FBI storage), Will goes into a mode whereby he knows what each next step in the checking of the cans will reveal: he 'knows' that photo stores send out cans for development; he 'knows' the label on one of the cans, under the label that says "Bob's Photo Store, Birmingham" will say, "Gateway Labs, St. Louis, Missouri." It becomes evident that the killer works at Gateway Labs.
