"He wasn't going to stop," FBI spokesman Eric Gonzalez said.
Keyes, 34, prepared a body disposal cache in the summer of 2011 for a future target, Gonzalez said. Murder kits also have been recovered in New York and Vermont.
In Alaska, authorities recovered the cache containing a shovel and two large bottles of Drano from Eagle River north of Anchorage. Gonzalez said the drain de-clogger would speed up decomposition of a body.
Keyes told authorities he killed barista Samantha Koenig and at least seven others over the past decade, including Bill and Lorraine Currier of Essex, Vt., in June 2011. The couple's bodies have not been found.
Keyes was found dead Sunday in his Anchorage jail cell after he killed himself by slitting a wrist and strangling himself with a rolled up sheet.
Before his death, Keyes said he sexually assaulted Koenig after abducting her in February from the coffee stand where she worked. He told authorities he then strangled Koenig and left here body in a shed outside his Anchorage house for two weeks while he went on a cruise.
When he returned, Keyes tied up Koenig and posed her body to make it look like she was still alive. He then took a Polaroid of her with a newspaper dated Feb. 13, which was 12 days after her abduction, according to the FBI.
Keyes made a photocopy of the picture and typed a ransom note on the back demanding $30,000 from Koenig's family. He then sent a text message to Koenig's boyfriend on her cellphone with directions to where he'd left the note at a local dog park.
Keyes dismembered Koenig's body and put it in a frozen lake north of Anchorage after drilling a hole in the ice with a chain saw, according to authorities.
He was arrested in Lufkin, Texas, in March after using Koenig's stolen debit card at ATMs there and in Alaska, Arizona and New Mexico. He was facing a March 2013 trial in Koenig's death.
Koenig's remains were found in April after Keyes told authorities where to look.
Keyes didn't identify any other victims or say where the remains were, other than to say four were killed in Washington state and one was killed on the East Coast, with the body disposed of in New York.
The FBI released new details about the discovery of weapons and other items connected to Keyes at an upstate New York reservoir.
FBI spokesman Paul Holstein said an April 18 search in the Adirondacks town of Parishville turned up a bucket containing a silencer, .22-caliber Ruger frame, ammunition and a flashlight, all linked to Keyes. Divers on April 24 found the bolt and barrel of a gun used during the killings of the Curriers. Divers found a gun owned by the Curriers on June 5.
Keyes owned property in the Adirondacks.
Gonzalez confirmed that Keyes buried a murder kit in the woods on the banks of the Winooski River in spring 2009 in Vermont, then dug up the cache two years later and used the weapons in the Vermont killings.
Keyes traveled extensively in the U.S., landing at one location and targeting victims randomly hundreds of miles away. Keyes told authorities he robbed several banks and used money he made as a general contractor to pay for his travels.
Koenig was an exception to the distance rule. Keyes had never seen the barista before but chose the coffee stand because of its location and because it stayed open later than other stands.
Anchorage police said Keyes also targeted others in Alaska before killing Koenig but always backed off before acting.
In May 2011, he focused on a couple at Point Woronzof, a popular park area along the Anchorage shorefront.
Lt. Anthony Henry, commander of the homicide unit, said Keyes backed off at the last minute after police inadvertently arrived during a routine patrol.