They were killed prior to Season One.
Two female victims were found dismembered in Broward County, Florida, within the past five months. A similar kill known as the Pool Victim was discovered afterward in nearby Dade County. Debra Morgan remarked that the earlier victims were "chopped up just like this one".
The identities of Victims 1 & 2 were unknown but likely they were prostitutes, just as were the later female victims of Brian Moser. However, they were not Brian's first victims. His earliest known kill was actually a New Jersey plumber by the name of Rudy Cooper. Brian had killed him back in 1998 in order to steal his identify.
While investigating, Angel Batista questioned a prostitute, known as Monique. She revealed to him that, a year beforehand, she had met with a john who was turned on by her prosthetic arm. Unfortunately, she didn't know his name (which was Brian Moser). Later, Brian arranged a second meeting with Monique. Before he murdered her, he told her that her "imperfection" was what had saved her the first time. This suggested that he had killed other prostitutes before the two women in Broward County.