Top left: Graham pulls some photos out of the Tooth Fairy case file while on an airplane flight; note the young passenger sitting to his left. (All images may be clicked to enlarge). Top right: The photos are from the victim families' home movies (Leeds family on left; Jacobi family on right). Above left: Later on during the flight, after Graham has been sleeping for a short while, we see some photos of the Leeds and Jacobi crime scenes on his tray, such as this photo of Mrs. Leeds' dead body, with mirror shards placed in her eye sockets. Above right: The young passenger is horrified upon happening to see the crime scene photos.
As shown in the above screencaps, there is a scene in Manhunter in which Will Graham is a passenger on an airplane, and at one point during the flight he pulls some photographs from the home movies of the two families who have been killed (so far) by Dollarhyde, the Leeds and Jacobis, out of his case file, and puts them up on his seat tray so he can look at them. Eventually he drifts off to sleep and has a dream of Molly and of working on a boat. Then after a short while, he is awoken by the screaming and crying of a young passenger next to him, and when he looks down we see that there are now different photographs of the two families on the tray: instead of the home movie stills, we see photos of the respective crime scenes showing the victims' bodies after they have been brutally murdered and mutilated - it's as if the families have 'gone from living to dead' due to Graham himself, as if he is the killer. As an aside, in Greek mythology, Thanatos, the personification of death, is the twin brother of Hypnos, the god of sleep. Mythology will come into play later in the analysis.
One of the strongest suggestions the audience is sent by the movie-makers, that Graham is like the killer, occurs in the scene in the Jacobis' back yard. At every turn during his investigation in this scene, Will knows what the killer was thinking and doing while he was in the yard; for example, Will sees a candy wrapper on the ground (above left), and then 'knows' to climb the rope leading up the nearby tree (above right). One might say that this would be normal investigative procedure for the police or FBI, but the point here is that Graham does not hesitate in performing these actions - he instead seems to be acting simply on his own natural initiative.