A body believed to be that of Samantha Koenig of Anchorage was recovered from Matanuska Lake, Mew said. City police, state troopers and FBI agents spent hours at the lake scene Monday.
Surveillance video on the night Koenig was last seen showed her being led away from her coffee stand by a man believed to be armed.
Police said they believe the Anchorage woman died within hours of her abduction, Mew told a Monday evening news conference.
"Investigators further believe the person responsible for Samantha's death acted alone, and we are confident that we have that person in custody," Mew said.
The only man who has been listed by Anchorage police as a "person of interest" in the abduction of Koenig was arraigned March 27 in federal court in Anchorage on a fraud charge, shortly after being returned from Texas, where he was arrested.
Israel Keyes, 34, entered a not guilty plea to a charge of access device fraud. Federal prosecutors say he made cash withdrawals from a stolen debit card.
The card was not Koenig's.
"We are working closely with the U.S. Attorney's Office, and charges for Samantha's kidnapping and murder will be forthcoming," Mew said.
"We would like to reiterate our request for information relative to the movement of the white pickup truck," FBI Special Agent in Anchorage Mary Rook said at Monday's news conference.
"Specifically, we want to hear from anyone who may have seen the truck in the vicinity of Matanuska Lake," she said.
Investigators earlier said they're looking for people who may have seen the truck in late January and early February near the midtown Anchorage coffee shack where Samantha Koenig worked as a barista and other locations.
The truck was equipped with green tool boxes that run the length of the box on each side.
It also was photographed with a rack over the box, but the truck may have been driven without it, investigators said.
FBI agent Darrin Jones last week said the rack may have been off of the vehicle at the time of the incident.
Keyes likely would have needed help moving the rack on or off the truck, and investigators would like to speak to anyone who may have assisted him.