Israel Keyes had told authorities he had traveled around the country for more than a decade, claiming that he killed at least four other people in Washington state and another in New York. Eight victims in all that authorities heard about.

And he was still talking, as late as last week. And on Sunday morning, he was dead. Authorities wouldn’t say how he killed himself, only that he was alone in his cell. They also did not say whether he left a note.

For now, authorities are trying to find out exactly who it was the one-man construction contractor killed.

So far, “there’s no indication that he was lying,” FBI spokesman Eric Gonzalez said, adding that Keyes’ DNA has been put in an FBI database available for other law enforcement agencies to use in their own investigations.

Officials believe there are more victims in other states, but acknowledge that they may never know who they were.

“We’re going to continue to run down leads and continue our efforts to identify his victims so we can bring some closure to the families,” said Mary Rook, the FBI supervisor in Alaska.

While under arrest in connection with the disappearance of 18-year-old barista Samantha Koenig, Keyes confessed to the deaths of Bill and Lorraine Currier, of Essex, Vt., who disappeared in June 2011, authorities said.

On Monday, officials confirmed at a news conference in Vermont that he was responsible for the Curriers’ deaths, saying Keyes described details that had not been released publicly.

Authorities in Alaska said say Keyes traveled extensively, driving hundreds of miles for victims after landing at a distant airport. Keyes flew from Alaska to Chicago with the intent of kidnapping and killing someone, drove to Vermont, picked the Curriers, a couple in their 50s, and broke into their home.

In their bedroom, Keyes told police, he bound them with zip ties, forced them into their car and drove them to an abandoned house, where he tied Bill to a stool in the basement, prosecutor T.J. Donovan said. Lorraine Currier tried to escape and Keyes ran out and tackled her. Her husband then tried to escape, prosecutors said.

Keyes shot Bill Currier with a gun he brought from Alaska, and then sexually assaulted and strangled Lorraine Currier, Donovan said, his voice breaking. Their bodies have never been found. “They fought to the end,” Donovan said, adding that the couple showed “extraordinary bravery and love for each other.”

Keyes told investigators he chose the Curriers’ home because it had an attached garage, no evidence of children or a dog and the style of the house clued him in to the probable location of the master bedroom

Prosecutors based their account largely on what Keyes said, but had some evidence to corroborate it.

Keyes previously lived in Washington state before moving to Alaska in 2007 to start a construction business. He also owned property in upstate New York, near the Canadian border.

Ayn Dietrich, a spokeswoman for the FBI in Seattle, said agents are reviewing unsolved murders across the state to determine whether Keyes might have been responsible for any of them.

The FBI has consulted with behavior specialists to develop insight into Keyes’ personality. Their analysis is incomplete.

But they know he was a loner who didn’t have a clear pattern in selecting victims. They varied in gender and age, from Koenig to the Curriers. Money didn’t seem to be a driving concern.

Authorities described Keyes as methodical, in the Currier case taking days to find the perfect victim. He was also thorough in disposing of victims’ bodies. Only Koenig’s body has been recovered.

As he talked to police, Keyes apparently was concerned about his reputation. Keyes told investigators he would stop talking to police if his name was released publicly in the Currier case.

“He was very, very, very sensitive to his reputation, as odd at that sounds,” Anchorage Police Chief Mark Mew said. “We had to keep things extra quiet in order to keep him talking with us.”

When he did, he did so with only a little information at a time.

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. Her disappearance gripped the city for weeks.

A surveillance camera showed an apparently armed man in a hooded sweat shirt leading her away from the coffee stand. Koenig’s friends and relatives set up a reward fund and plastered the city with fliers.

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. 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. Keyes could have faced the death penalty in her case.

Koenig’s family said there was no apparent previous connection between the teenager and Keyes. Reached by phone Sunday, Koenig’s father, James Koenig, declined to comment on Keyes’ death.

Marilyn Chates, Bill Currier’s mother, said 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. 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.