Alaska State Police spokeswoman Beth Ipsen said troopers were called to the Anchorage jail about 6:30 a.m. after Israel Keyes' body was found in his cell, the Anchorage Daily News reported. She said troopers determined his death was "an apparent suicide" but declined to describe how he killed himself, the newspaper said.
"I can tell you that he was alone in his cell. ... We don't suspect foul play," Ipsen said.
Keyes was jailed in the kidnapping and killing of Samantha Koenig, 18, who disappeared Feb. 1, and was suspected in at least seven other deaths in other states.
FBI Special Agent in Charge Mary Rook disclosed authorities believe Keyes killed William and Lorraine Currier, a Vermont couple who disappeared in June 2011 and was responsible for four deaths in Washington state and one in New York.
Rook said authorities didn't have the names of the suspected victims in New York and Washington.
Koenig's body was found April 2 in Matanuska Lake north of Anchorage.
Authorities said Sunday Keyes confessed to killing her and the Curriers. No other bodies have yet been found, authorities said.