The Ice Truck Killer staged a bloodbath in Room 103 by using the blood he had collected from his victims.
Miami Metro Homicide receives a jar of blood, in which floats a hotel key marked Marina View Hotel - Room 103. The police find the hotel room full of blood, but no bodies.
When Dexter enters the blood soaked room, he suddenly has flashbacks of himself as a small child in the Shipping Yard, watching his mother, Laura Moser, being chainsawed to death. Dexter experiences a panic attack and collapses into the blood. Unable to continue examining the crime scene, he hurries out of the hotel. Dexter claims to his coworkers that he skipped breakfast and feels ill from the effects of low blood sugar. After he calms down, Dexter reenters the hotel and sits outside the room, instructing Vince Masuka to take "lots and lots of photos."
During their investigation of the room, Debra and Doakes discover that the radio is tuned to 103 FM and the room's Bible is bookmarked for Leviticus 10:3. (The number 103 refers to the date a newspaper was published (October 3, 1973) with an article about the murder of Dexter's mother (October 2, 1973).
Later, Dexter returns to Room 103 by himself and remembers more of his mother's murder.