Adam Matthew Moss, 23, stared at the floor or his hands as he appeared before Woodbury County District Judge Frank B. Nelson.
Seven first-degree murder accusations were detailed in complaints filed by county prosecutors, who said formal charges would be filed this coming week. If convicted of a single first-degree murder charge, Moss would face life in prison; Iowa does not have the death penalty.
No motive was given for the killings.
Moss showed no reaction in court and never raised his eyes.
The judge said Moss is accused of going into the home of his girlfriend, Leticia Aguilar, late Monday or early Tuesday, while she and her children were sleeping.
He is accused of beating each of the children to death with a hammer while they slept, then going to Aguilar's room, cutting her throat and beating her in the face with a hammer, Nelson said.
The bodies of Aguilar, 31, and Claudia, 12; Zach, 11; Larry, 9; Lisa, 7; and Michael, 6, were found Thursday evening by a baby sitter who dropped by to see why the children had failed to show up at her home after school.
About the same time, the body of Ronald E. Fish, 58, owner of a tire store and service station, was found at his home some two miles away. Moss also is accused of stealing Fish's car.
Fish was attacked with a hammer and a knife late Wednesday or early Thursday, authorities said.
Moss himself is the only link between the two sets of victims, reports CBS News Correspondent Cynthia Bowers: the boyfriend of the children's mother, and a friend of Fish.
Following an all-night search, Moss was arrested Friday. He was found hiding behind a pile of plywood outside a shack that police had been watching, Police Chief Joe Frisbie said.
"This community was scared to death," Frisbie said. "Everyone was worried about their children and the schools and wondering if they were safe in their homes."
The judge said a public defender would be appointed for Moss.
He was being held Saturday under suicide watch in the Woodbury County jail, where he was isolated for his own safety, Sheriff Dave Amick said.
Perri Harper, a neighbor of Aguilar's, said there had been an argument at the house Tuesday night.
Moss had been living with Aguilar for a couple of months, said neighbor Myrtle Cress. The two had both worked at Smurfit-Stone Container Co., which makes cardboard and paper products.
Michael, Lisa and Larry were in the first, second and fourth grades at Everett Elementary School, principal Michaela Hansen said. On Friday, counselors spoke with children at that school and at West Middle School, which Claudia and Zach attended.
"They were truly wonderful kids," Hansen said. "My heart just goes out to that family. Words cannot express how badly I feel."
Williams said the traedy was especially hard for the children's classmates to understand because of the number slain.
"There is always trauma for kids when a favorite teacher is lost due to sudden death," he said. "There's trauma when a parent or close friends are lost. Here we have classmates - and a large number of them - who are dead."
Neighbors said Moss could be friendly and helpful but had a history of violence. His own brother had filed a restraining order against him last week claiming Moss had threatened him and his fiance. His mother said a former girlfriend, with whom he had a 4-year-old daughter, also had a restraining order against him.
Fred Scaletta, spokesman for the Iowa Corrections Department, said Moss was sentenced to a year of probation in 1995 for assault. The next year, he was placed on two years' probation for burglary and theft.
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