Detectives in Clark County, Washington, have announced that new DNA samples link two cold cases to convicted killer Warren Forrest, according to KOIN.

The Columbian reports that blood on a weapon used by Forrest, 68, was found to belong to Martha Morrison, 17. The missing Portland girl’s body was found in a remote area in Vancouver, Washington, in 1974. Morrison’s remains were recovered near the body of Carol Valenzuela, a young wife and mother Forrest is also suspected of killing.

Investigators originally believed that a blood stain on an air pistol belonged to Krista Blake, 19. Authorities now report, however, that Forrest attacked and raped Blake before burying her alive. Forrest is currently serving out a life sentence for the brutal 1974 atrocity.

Forty years later, authorities are now saying the air pistol was also involved in Morrison’s murder. And, according to the Washington State Crime Lab, the likelihood that the DNA test is wrong is approximately 1 in 30 billion, it has been reported.

Clark County Major Crimes Sergeant Duncan Hoss told The Columbian that, based on the proximity of the women’s bodies, Forrest could be implicated in Valenzuela’s murder.

Detectives believe Forrest is a serial murderer with as many as six victims. However, the 68-year-old has denied killing Valenzuela, Morrison, and several other women, according to The Oregonian.

The DNA shocker comes weeks after a review board denied Forrest for parole and ordered him to serve another seven years in prison, as reported by KOIN. In early August, the Washington Indeterminate Sentence Review Board determined that the inmate is “too high of a risk to release and not fully rehabilitated or a fit subject to release,” records indicate.

Sergeant Hoss said they intend to have a probable cause statement to prosecutors next week.

[Featured Image: Washington Department of Corrections]