The man described as a "person of interest" in the murders and disappearances of members of one northern Idaho family contacted authorities Wednesday afternoon. It was not clear if two children who were last seen on Sunday were with him.

Robert Roy Lutner (search), 33, was seen near the home of Brenda Kay Groene, 40, on Sunday, the day she, her son Slade Vincent Groene, 13, and her fiancé, Mark Edward McKenzie, 37, are believed to have been killed. Their bodies were found in the Groenes' home in Coeur d'Alene (search) on Monday.

The two youngest Groene children, Shasta Kay Groene (search), 8, and Dylan James Groene (search), 9, were last seen on Sunday. An Amber Alert was issued belatedly Tuesday morning for Shasta, 3-foot-10 and 40 pounds with long auburn hair and hazel eyes, and her brother, 4 feet and 60 pounds with a blond crew cut and blue eyes.

Authorities had been interested in speaking to Lutner, believed to have been known by the Groenes, after he was seen near their home. He was not described as a suspect.

"He may have seen something, he may have met somebody as he was leaving the residence," Capt. Ben Wolfinger of the sheriff's office said. "That's the kind of information we hope to glean from him."

Wolfinger said he could not disclose where Lutner was. Police had been seeking him since Tuesday, and investigators were planning to interview him.

He also said Lutner knew police were looking for him, but it was unclear if the children were with him.

"I don't know about the children. That is the first question our detectives are going to ask him, obviously," Wolfinger said.

The three victims had been bound and there was blood splattered in the house, indicating homicide.

Authorities believe the three were killed Sunday night. Autopsies to determine the exact times and causes of death should be completed by the end of day, Wolfinger said.

"There is a lot of blood. We don't know whose blood we're dealing with," he added, saying DNA results may not be available for several days.

Lutner has a record of minor traffic violations, misdemeanor drug offenses and has been convicted of unemployment fraud, Wolfinger said.

Brenda Groene has also reportedly had problems with drug use. Toxicology results would not be available for at least 10 days.

Lutner was on probation for the fraud charge, and told his probation officer Tuesday that he was going to see his father and stepmother in Boise. However, his stepmother told police she had not heard from him, Wolfinger said.

As the murders reached the 72-hour mark, local authorities, joined by FBI investigators and experts from nearby Spokane, Wash., were working overtime to find the two children.

"The children are our No. 1 priority," Wolfinger said.

Authorities expanded the search area around the Groenes' home to 400 acres. Dogs and police on horses and all-terrain vehicles were being used to find evidence of the children's whereabouts.

Wolfinger said the deep brush, marshy land and woods around the home made investigators' search no simple task. A few ponds on the land were to be drained.

"We want to search every nook and cranny — we know kids like hiding places," he said, touching on one theory that the children witnessed the murders and ran away. "We don't know how they just vanished. We don't know if they're injured, or if they got so scared they've gone someplace to hide out.

"Seventy-two hours is a long time," he added. "It's getting bleaker and bleaker."

Police have received more than 150 tips, and county officials were among those volunteering to man phone lines, Wolfinger said.

An Amber Alert issued in Idaho and several neighboring states was delayed more than one hour because an official questioned whether the children's disappearance warranted the alert. With no information on a suspect, the Washington State Patrol declined to broadcast the alert altogether, the Spokesman-Review reported.

The family lived in a house on a frontage road off Interstate 90 about eight miles east of the northern Idaho resort town. Both of the children lived at the house with their mother.

Jesse Groene, the children's 18-year-old brother, told FOX News on Wednesday he was baffled at the crimes against his family.

"I do not know anybody sick and demented and twisted enough to do something like this," he said from jail. Groene is being investigated for assault, battery, burglary and possession of stolen property, according to a jail employee who refused to give his name.

"My family got along with everybody, there were no enemies of our family, my family was just good people," Groene said. "It's just mind-boggling to think someone could do something like this."

The children's father, Steven Vincent Groene, 47, is not believed to be responsible for the killings or the disappearance of the children, Sheriff Rocky Watson said earlier Wednesday. Investigators have talked with him and described him as distraught.

"The lead detective told me he was ruled out," Watson said. "I didn't ask for details of why he was ruled out."

County court records indicate the family had minor scrapes with the law, including arrests of Brenda Groene for investigation of drug possession in June 2003 and for investigation of passing bad checks; drunken driving and driving without privileges and without insurance.

At Fernan Elementary School, attended by the missing children, no general announcement was made but counselors were available Tuesday, school officials said.

At Lakes Middle School, which the slain boy attended, Principal Chris Hammons said he visited every classroom to discuss the case.

"Many of the kids knew him, so they're grieving," Hammons said.

Steven and Brenda Groene were separated in 1998 and divorced in 2001. She had custody of the three younger children and he had custody of two older children, Vance Robert, now 20, and Jesse, 18, court records show.

"None of it can even begin to make sense," Vance Groene told television reporters. "They've always been taught don't talk to strangers, they never left the yard.

"The only thing I really have to look forward to in this situation is a positive outcome with my brother and my sister," he added.

Neighbor Janie Riley, who with her husband owns a nearby campground where the younger children often played, said she did not recall any obvious signs of trouble at the house.

"But there was a lot of activity going on there," Riley said.

Brenda Groene once operated Maid To Order, a house-cleaning business, and was on probation for possession of drug paraphernalia at the time of her death, reported The Spokesman-Review of Spokane.

She previously served time in jail and was ordered to get drug and alcohol counseling, but had trouble meeting that requirement because she lacked money to pay for it, court records indicated.

Authorities were called about 6:15 p.m. Monday by Bob Hollingsworth, a neighbor who had gone to the house to pay the 13-year-old for mowing his lawn over the weekend and noticed something was amiss, Wolfinger said.

Hollingsworth said he noticed dogs barking, the door of a vehicle open and none of his neighbors in sight.

"I had a bad feeling," he said. "There was always a kid or dog or something that comes out of there."

Glenn Kimball, who is building a house nearby, told The Spokesman-Review that the last time he saw Brenda Groene and her two younger children, they were planting trees and burning yard waste Saturday. Wolfinger said the children had not gone to school Monday.

The Associated Press contributed to this report.