Infamous Alaska serial killer Robert Hansen died Thursday morning at an Anchorage hospital, according to the Department of Corrections.

Hansen died around 1:30 a.m. at Alaska Regional Hospital, Sherrie Daigle, deputy director of the Department of Corrections, said. He had been transferred to the hospital on Wednesday. Cause of death will be determined by the medical examiner, but it appears he died of natural causes, she said. He had been in declining health for the past year, according to a press release.

Hansen had been moved from the Spring Creek Correctional Center in Seward to the Anchorage Correctional Complex on May 11, Alaska Dispatch reported at the time. Hansen, 75, had been placed in medical segregation in Anchorage, which is akin to being in the hospital, Daigle said then. Anchorage's jail is one of the state's only correctional facilities with a medical unit.

Hansen had received a 461-year sentence in February 1984, pleading guilty to the murders of four women. Hansen had confessed to authorities that he had killed 17 women and raped another 30 women over more than a decade.

Read more: 'Frozen Ground' serial killer Hansen dead