The father of two children who disappeared after the bludgeoned bodies of three family members were found in their Idaho home told FOX News that authorities do not believe he was telling the truth after giving him a polygraph test.

Steven Groene (search), 47, said it feels "pretty devastating" to be doubted over such serious allegations. In an interview with FOX News' Geraldo Rivera, Groene said he was asleep between 10 p.m. last Sunday and 6 a.m. Monday, the period in which police believe the crimes took place. He also said he and his ex-wife, Brenda Kay Groene (search), 40, had had a severe argument over his request to make an unscheduled visit to the two children, Dylan and Shasta, two days earlier.

Steven Groene maintained his innocence and reminded everyone he volunteered to take polygraph, DNA (search) and urine tests.

"They don't think I'm being truthful" about not knowing where the children are, he said of authorities after the lie-detector test was administered.

"[The test administrator] said, 'You know something about the whereabouts of your children?' I said, 'No way," he said. He added that he was truthful about his history of alcohol and drug use.

On Friday, investigators concluded the crime scene investigation at the home. Also on Friday, a tip was dismissed that the youngsters were in a van about 20 miles from the Canadian border. Sheriff's Capt. Ben Wolfinger said the boy in the van had long hair, but the boy being sought has a crew cut.

Dylan James Groene, 9, and his sister, Shasta Kay Groene, 8, were last seen May 15 at their rural home near Coeur d'Alene.

The next evening, their mother, 13-year-old brother, Slade Vincent Groene, and the mother's boyfriend, Mark Edward McKenzie, 37, were discovered bound and bludgeoned to death in the white cinderblock home.

Searches of about 400 acres of brush and woods near the house wrapped up Thursday, and divers used their hands to feel the bottoms of nearby ponds and streams.

"They're confident there's nothing more here," Wolfinger said. "Ground crews are 100 percent certain the children are not here."

Kootenai County Coroner Dr. Robert West told Spokane, Wash., said preliminary toxicology results indicated the presence of "illicit drugs" in the two adults, but not in the 13-year-old. He did not elaborate.

Detectives contacted everyone known to have attended a barbecue at the home Sunday and detectives were taking statements from them, Wolfinger said. He declined to say how many were questioned or what was learned.

If you have any information on the whereabouts of Dylan and Shasta Groene, please call the Kootenai County Sheriff's Office at 208-446-1300/2292.

FOX News' Geraldo Rivera and The Associated Press contributed to this report.