Keyes was scheduled to go on trial in March for the February death of Samantha Koenig.
At a press conference Sunday U.S. Attorney Karen Loeffler confirmed that Keyes had not only confessed to Koenig's murder, but had been linked to seven other killings in three other states.
Keyes had also confessed to the murders of Bill and Lorraine Currier of Essex, Vermont, who were last seen leaving work on June 8, 2011. Their bodies have never been found.
Keyes also told investigators that he killed four people in Washington State and another person in New York, but he never revealed the victims' names or other details.
Massive Search Launched
Keyes was caught on videotape armed and wearing a hooded sweatshirt leading Koenig away from the coffee stand where she worked as a barista. Her disappearance set off a massive search for the teenager as her friends and relatives offered a reward in her case and posted flyers throughout the Anchorage area.
Police said after Keyes killed Koenig, he used her cell phone to send a text message in an attempt to cover up her kidnapping. He then flew to Texas.
Keyes returned to Anchorage on Feb. 17 and sent another text message demanding ransom money be deposited in the account of a debit card that he stole from the car Koenig was driving. Prosecutors said he obtained the PIN for the account and scratched it on the back of the card.
Body Found in Lake
Keyes was arrested in Texas after he used Koenig's debit card to make cash withdrawals in Alaska, Arizona, New Mexico and Texas. He was initially returned to Alaska to face charges unrelated to Koenig's kidnapping, but was indicted April 2 for her abduction.
Koenig's body was not found until April 2, two months after she was abducted, by a forensic dive team in Matanuska Lake north of Alaska.
At the press conference, FBI Special Agent Mary Rook said authorities may never know how many people Keyes killed. There may be other victims in other states that he did not reveal.
Rook said Keyes only gave investigators bits of information at a time about his crimes, withholding names and locations.
Get the Crime & Punishment Newsletter