Dylan and Shasta were declared missing May 16 after police found the bound and beaten bodies of their mother, their older brother, and their mother's boyfriend. Shasta was discovered July 2 in a local diner with James Edward Duncan III, a registered sex offender who had fled Fargo, N.D.
After questioning Shasta, authorities said they believed Dylan was likely dead, and human remains thought to be Dylan were found last week in western Montana. The confirmation was made public Sunday.
"According to the FBI lab in Quantico, Va., the remains found last week in Montana have been positively identified as Dylan Groene," Sheriff's Capt. Ben Wolfinger said.
Wolfinger says the investigation continues into the kidnapping of Dylan and his eight year old sister Shasta, CBS News correspondent Stephan Kaufman reports. Wolfinger said authorities will be careful not to jeopardize their case against Duncan.
Duncan was held without bail in the Kootenai County Jail on two kidnapping charges. Authorities believe he also is the sole person responsible for the deaths of Brenda Kay Groene, 40; Slade Groene, 13; and Mark Edward McKenzie, 37, in the Groenes' rural Coeur d'Alene home.
Sheriff Rocky Watson has said he believes the motive for the killings was to acquire the children for sex. Watson also said authorities believe the family was chosen at random, but that the attack was carefully planned and executed.
Duncan, 42, was on the run from a child molestation charge in Minnesota. Public defender Lynn Nelson on Thursday filed a bail reduction request that will be heard at a July 19 hearing at which Duncan is expected to enter a plea.
Kidnapping in Idaho can carry the death penalty, but authorities have not decided whether to seek that punishment and do not have to make a formal decision until 30 days after a plea is entered. Duncan also may face federal charges.
Shasta has been released from Kootenai Medical Center to her father, Steve Groene.