The Spokane County Sheriff's Office on Tuesday identified Douglas R. Perry, 60, as a person of interest in the case. He would have been 37 and 38 at the time of the killings, the sheriff's office said.
"Detectives are searching for anyone that may have purchased a firearm from Perry" in the 1990s, the sheriff's office said in a statement.
Perry was identified through DNA evidence found under the fingernails of one of the victims, sheriff's spokesman Craig Chamberlin said.
The suspect is a transgendered woman also known as Donna Perry, Chamberlin said. Perry was already in the Spokane County Jail on an unrelated federal charge, he said.
The sheriff's office is working with Spokane police on the case.
The body of Yolanda Sapp, 26, was discovered on Feb. 22, 1990. The body of Nikkie Lowe, 34, was discovered on March 25, 1990. The body of Kathlene Brisbois, 38, was found on May 15, 1990.
All three women, who worked as prostitutes, had been shot with a small caliber handgun, the sheriff's office said.
Police have said that all the victims were nude when found at locations in or near the Spokane River.
Detectives would like to speak with associates of the three victims and of Perry.
Douglas Perry had gender reassignment surgery in 2000 in Bangkok and is now known as Donna Perry, according to court documents.
Advances in DNA technology prompted law enforcement officers to resubmit some evidence collected from Brisbois' fingernails for testing in 2009, Chamberlin said. The DNA came back as belonging to a male, but did not match anyone in the federal database of convicted felons.
A major break came on Sept. 14, when a Washington State Crime Laboratory technician found that the evidence from Brisbois matched the DNA of Perry, who was in federal custody after he was arrested in Spokane on a weapons charge in March.
In October, law officers confirmed that Perry's fingerprints were found on an item recovered in the Lowe homicide.
"Those latent fingerprints were compared to Douglas Perry by the Spokane Forensic Unit and they matched the index and middle finger of Douglas Perry," according to a search warrant unsealed Tuesday in the case.