Gary Ridgway, the Green River Killer, was booked Monday, Sept. 9 into the King County Correctional Facility in Seattle after a transfer from the state prison in Walla Walla.

Few details have been released about why Ridgway is back in King County, although it might be for another murder case. He is serving 49 consecutive life sentences for murder.

“Since Gary Ridgway’s arrest in 2001 pertaining to the Green River murder investigation, the King County Sheriff’s Office continues to actively investigate potentially related cases,” said a Sheriff’s Office spokesperson when about why Ridgway is in custody in King County.

The spokesperson didn’t share any further details or if the Sheriff’s Office might file another murder case against Ridgway. The King County Prosecuting Attorney’s Office referred any questions from the media to the Sheriff’s Office.

Ridgway was booked on an institutional hold into the county jail, according to jail records. An institutional hold means he must be returned to state custody. State Department of Corrections records list Ridgway as an inmate at the state prison in Walla Walla.

King County Sheriff’s Office detectives arrested Ridgway in 2001 because of DNA evidence that connected him with four of the 49 killings, which began in 1982 and ended in 1998. Ridgway is serving 49 life sentences without the possibility of parole. He strangled each of his victims.

Detectives believe he might have killed as many as 65 to 70 women.