He 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. Authorities wouldn't say how he killed himself, only that he was alone in his cell. An autopsy will be conducted.
While being investigated in the Koenig disappearance, Keyes also confessed to the deaths of Bill and Lorraine Currier, of Essex, Vt., who disappeared in June 2011, authorities said. Officials confirmed Monday at a news conference in Vermont that he was responsible, saying he described details that had not been released publicly.
Keyes flew from Alaska to Chicago with the intent of kidnapping and killing someone, drove to Vermont and picked the Curriers, a couple in their 50s, at random, officials in Vermont said. He told police he broke into their home, went into their bedroom, bound them with zip ties and forced them into their car.
He then drove them to an abandoned house and tied Bill to a stool in the basement, while Lorraine Currier tried to escape, Chittenden County state's attorney T.J. Donovan said. Discovering this, Keyes ran out and tackled Lorraine, and Bill then tried to escape.
He shot Bill Currier with the gun he had stolen from the couple's home, and then sexually assaulted and strangled Lorraine Currier, Donovan said, his voice breaking. Their bodies have never been found, and Keyes did not volunteer the information.
"They fought to the end," Donovan said, adding that they showed "extraordinary bravery and love for each other."
Keyes could have faced the death penalty in the Koenig case.
He 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. He didn't have a clear pattern in victims, who ranged widely in age, authorities said.
There may be victims in other states, besides the four states noted by Keyes, said FBI agent Mary Rook. Keyes also confessed to bank robberies in New York state and Texas.
Authorities said they may never know the full extent of his crimes because he parsed out only a little information at a time, withholding names and locations of most of his victims.
Money appeared to be just a partial motive, authorities said. In the Vermont case, Bill Currier's wallet had been left behind at their home, but Lorraine Currier's purse was missing.
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.
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 on 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.