Israel Keyes, who had also confessed to killing a Vermont couple, was found dead in his cell Sunday, authorities said at a news conference that included U.S. Attorney Karen Loeffler, the FBI, and Anchorage police.
Keyes was facing a March trial in Anchorage federal court for the murder of 18-year-old Samantha Koenig, who was abducted from a coffee kiosk in the city last February. He was later arrested in Texas after using the victim's debit card.
Anchorage police chief Mark Mew said Keyes confessed to killing Koenig, as well as killing Bill and Lorraine Currier of Essex, Vt.
The bodies of the Curriers have never been found. They were last seen leaving their jobs on June 8, 2011. Co-workers reported them missing the next day.
Keyes didn't have a clear pattern in victims, who ranged widely in age, authorities said. Money appeared to be just a partial motive.
Authorities say they may never know the full extent of Keyes' crimes because he parsed out only a little information at a time, withholding names and locations of most of his victims.
Keyes, 34, also indicated he killed four others in Washington state and one person in New York state, but didn't give the victims' names, authorities said.
Authorities wouldn't say how Keyes killed himself, only that he was alone in his cell. An autopsy will be conducted.
Keyes could have faced the death penalty in the Koenig case.
The FBI contends Keyes killed Koenig less than a day after she was kidnapped. Her body was recovered April 2 from an ice-covered lake north of Anchorage.
Koenig's disappearance gripped the city for weeks.
A surveillance camera showed an apparently armed man in a hooded sweat shirt leading Koenig away from the coffee stand. Koenig's friends and relatives established a reward fund and plastered the city with fliers with her photo in hopes of finding the young woman alive.
Prosecutors said Keyes stole the debit card from a vehicle she shared that was parked near her home, obtained the personal identification number and scratched the number into the card.
After killing Koenig, Keyes used her phone to send text messages to conceal the abduction, according to prosecutors. He flew to Texas and returned Feb. 17 to Anchorage, where he sent another text message demanding ransom and directing it to the account connected to the stolen debit card, according to prosecutors.
Keyes made withdrawals from automated teller machines in Alaska, Arizona, New Mexico and Texas before his arrest in Texas, according to prosecutors. He was charged with kidnapping resulting in Koenig's death.
Koenig's family said there was no apparent previous connection between the teen and the suspect. Reached by phone Sunday, Koenig's father, James Koenig declined to comment on Keyes' death.
In Vermont, the U.S. Attorney's Office said in a statement Sunday that they have been working with investigators in Alaska since April on the Currier case.
Investigators have determined that the couple's home was entered forcibly, and that there was evidence of a possible struggle.
Their car was stolen and was recovered several days after their disappearance at an apartment complex about three-quarters of a mile away from their home.
Marilyn Chates, Bill Currier's mother, told The Associated Press that police contacted her some time ago to tell her about Keyes' confession and to tell her that they believed the couple's killing was random.
Certificates of presumed death were issued over the summer and a memorial service was held in late summer, she said.
Vermont authorities called Chates Sunday to tell her of Keyes' suicide.
"After some thinking, our family has been saved the long road ahead - trials, possible plea agreements and possible appeals - and perhaps this was the best thing that could have happened," she said from her home in Florida Sunday evening.
Keyes was thorough and methodical in disposing victims, authorities said Sunday. Only Koenig's body has been recovered.
There may be victims in other states, besides the four states noted by Keyes, FBI Special Agent in Charge Mary Rook said.
Keyes also confessed to bank robberies in New York state and Texas.
Associated Press writer Rebecca Miller in Philadelphia contributed to this report.