ANCHORAGE, Alaska — Trying desperately to identify Alaska-based serial killer Israel Keyes’ unknown victims, federal authorities have released new information from the Keyes investigation files.

Once a self-employed carpenter living in Anchorage, Keyes is thought to have killed 11 people across the United States from 2001 to 2012, the FBI said in a written statement Monday. Keyes lived in Maine on the outskirts of an Amish community while growing up in the 1990s.

Keyes burglarized 20 to 30 homes across the country and robbed several banks during that time period to fund his hobby of killing people, according to the FBI.

“In a series of interviews with law enforcement, Keyes described significant planning and preparation for his murders, reflecting a meticulous and organized approach to his crimes,” the FBI statement says. “Investigators believe Keyes did not know any of his victims prior to their abductions.”

His last known victim — the one that got him caught — was Anchorage resident Samantha Koenig. Keyes abducted the 18-year-old from a coffee hut in Anchorage the night of Feb. 1, 2012, and strangled her in a shed outside his girlfriend’s house in Anchorage, where he lived, according to police and federal prosecutors.

The FBI revealed Monday that Keyes is thought to have killed another person in Texas after the Koenig murder.

While in Texas, Keyes made repeated bank withdrawals using a debit card he stole from Koenig. Authorities tracked him down and arrested him there in March 2012, and federal agents extradited Keyes back to Anchorage. Keyes told investigators that prior to killing Koenig, he had slain a couple in Vermont — Bill and Lorraine Currier — in June 2011.

Keyes also talked about committing other prior abductions and murders, offering varying degrees of detail about each, but the investigators were never able to determine the names of the victims in those cases, FBI spokesman Eric Gonzalez said Monday.

“He described several remote locations that he frequented to look for victims — parks, campgrounds, trail heads, cemeteries, boating areas, etc.,” the FBI statement said. “Keyes also admitted to frequenting prostitutes during his travels and it is unknown at this time if he met any of his victims in this manner.”

Keyes claimed the slayings occurred in fewer than 10 states, though “it is not unlikely” that he flew to one state, drove to another and disposed of the victims’ bodies somewhere else, Gonzalez said. Other than the Curriers and Koenig, none of the other cases drew much media attention, Keyes told the investigators.

Other crimes Keyes committed might not have even happened in the U.S., the FBI said. He is thought to have traveled internationally and, while living in upstate New York for a time, might have entered Canada.

“He reported several trips to Montreal in which he sought out prostitutes,” the FBI said.

Unfortunately, Gonzalez said, Keyes took his own life in his jail cell last year and the secrets of his crimes went to the grave with him.

“At this point, this investigation is all about identifying the possible victims and bringing closure to their families,” Gonzalez said. “What makes this difficult is that, when it comes to the victims, it could be anyone. Male, female, young, old. They were more victims of opportunity than, say, fitting a certain victimology profile.”

“I guess people expect a serial killer to behave a certain way,” Gonzalez said. “But they’re all different.”

The decision to release the four-page statement on the Keyes’ investigation Monday is “our last best hope of identifying victims,” Gonzalez said.

“At this point, we’ve exhausted all of our investigative leads, so there was no investigative advantage to holding onto this information,” Gonzalez said.