In Vermont, the U.S. Attorney's Office said in a statement Sunday that they have been working with investigators in Alaska since April on the Currier case.
Investigators have determined that the couple's home was entered forcibly, and that there was evidence of a possible struggle.
Their car was stolen and was recovered several days after their disappearance at an apartment complex about three-quarters of a mile away from their home.
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 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.
He didn't have a clear pattern in victims, who ranged widely in age, authorities said. Money appeared to be just a partial motive.
Authorities say they may never know the full extent of Keyes' crimes because he parsed out only a little information at a time, withholding names and locations of most of his victims.
There may be victims in other states, besides the four states noted by Keyes, FBI Special Agent in Charge Mary Rook said.
Keyes also confessed to bank robberies in New York state and Texas.
Authorities wouldn't say how Keyes killed himself, only that he was alone in his cell. An autopsy will be conducted.
Keyes could have faced the death penalty in the Koenig case.
Associated Press writer Rebecca Miller contributed to this report.