Keyes confessed to other killings without identifying the victims or saying where their remains were, other than that four were killed in Washington state and one in New York.
Keyes, who faced a March trial in Koenig's death, was found dead in his Anchorage jail cell Sunday after he apparently killed himself.
Also Tuesday, authorities released video footage of Keyes abducting Koenig, caught by a surveillance camera.
In the video, Keyes wears a black ski mask as he climbs through the window of an Anchorage coffee kiosk. He then orders an Americano coffee, which Koenig makes.
Afterward, Koenig is seen putting her hands up several times before Keyes uses zip ties to bind her hands behind her back and leads her out.
Keyes told Koenig he would let her go if her family paid a ransom, but that was never his intention, police said.
"He knew all along he was going to kill her," Anchorage homicide Detective Monique Doll said.
Koenig's body was recovered from the lake in April.
Another video released Tuesday shows a man identified as Keyes getting out of a white truck parked in nearby parking lot just before the abduction took place, and returning with another person he appeared to gripping tightly.
Police said Tuesday a license plate, green toolboxes and a ladder rack had been removed from the pickup truck before the abduction, then reinstalled afterward so Keyes could disguise the vehicle, which had an extended bed.
In their investigation, the vehicle appeared twice in a list of 750 local white trucks of the same kind, but police scratched it off the list of possibilities because it looked so different.
Authorities say Keyes traveled extensively in the U.S., landing at one location and targeting victims randomly hundreds of miles away. In the Koenig case, he stuck to his own town.
"He broke his own rule," Doll said.