The announcement from the Kootenai County Sheriff's office left Dylan's sister, Shasta, 8, as the only survivor of what Sheriff Rocky Watson believes was an attack intended to abduct the children for sex.

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.

"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 Sunday. He said investigators continue to follow other leads.

Wolfinger declined to provide more details or answer questions at the brief Sunday news conference, citing the ongoing investigation and sensitivity for the Groene family.

Duncan is 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.

In an interview earlier Sunday, Wolfinger declined to comment on a newspaper report that the three were killed with a hammer.

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. Prosecutors have acknowledged that Duncan ultimately may face federal charges.

Shasta has been released from Kootenai Medical Center to her father, Steve Groene.