An admitted serial killer who committed suicide as he was awaiting trial for murdering an Anchorage barista is believed to have killed at least 11 people across the country or even outside the U.S., American law enforcement officials said on Monday.

Investigators believe Israel Keyes murdered his first victim in 2001 and his last in 2012 when he kidnapped 18-year-old Samantha Koenig of Anchorage, strangled her and dumped her remains in an icy lake.

The FBI released a detailed timeline of Keyes' travels and confessed crimes, which also included cases of robbery, arson and rape.

"Right now, the best hope for solving these cases is going to come from information from the public," said Assistant U.S. Attorney Kevin Feldis, who led the prosecution of Keyes.

Keyes was arrested on March 13, 2012, in Lufkin, Texas, in connection with Koenig's disappearance from the Anchorage coffee stand where she worked.

About four weeks earlier, he confessed to burning down a house in Aledo, Texas, and robbing a bank in Azle, Texas, according to the new details released by investigators.

The 34-year-old carpenter and army veteran killed himself in his Anchorage jail cell on Dec. 2 or 3. His suicide ended the criminal case, but not the investigation, which will continue "as long as there are unsolved murders that he may be responsible for," said Feldis.

Investigators believe there are 11 victims based on interviews with Keyes, in which he confessed to multiple murders but put the number at "less than a dozen," Feldis said.

"Was he referring only to the United States? Could there be victims outside the country? I think there could be, but we don't know," Feldis said.

Travelled to Canada often

Keyes travelled to Canada often, to Mexico in 2007 and 2008 and to Belize in 2005. He frequented prostitutes in Montreal and elsewhere, officials said.

Keyes's only known victims are Koenig and a Vermont couple that he confessed to killing in 2011, Bill and Lorraine Currier.

His other victims may include a woman murdered in 2009 from the East Coast. Keyes also admitted to dumping one body into Crescent Lake in Washington state.

Police suspect Keyes murdered someone in Texas because he gave evasive answers about his activities and whereabouts, Feldis said.

"He described to us being really amped up during the time he was in Texas and being out looking to do something," Feldis said.

Keyes claimed Koenig was his last murder victim, Feldis said.