The parents accused of beating their 12-year-old daughter to death have told police they were meting out the biblical punishment of "40 lashes minus one, three times," detectives said Monday. Constance Slack, a registered nurse at a children's hospital, gagged her daughter, Laree, while she was strapped down to a futon, police said. Her father, Larry Slack, then repeatedly hit the child with an inch-thick section of rubberized electrical cable filled with strands of wire, police said. She died of internal bleeding.

"It was horrific,'' one seasoned police officer said.

The parents were upset that Laree was being "uncooperative" after they ordered their chilldren to find a smock with credit cards inside Saturday night, police said. Larry Slack is a firm believer in corporal punishment, and he and his wife decided to administer discipline from the Bible, investigators said.

"It was his attempt to teach his daughter about responsibility,'' Area 2 Sgt. Stan Salabura said.

Both parents are devout Jehovah's Witnesses who home-schooled their six children, ages 8 to 17, police and neighbors said.

"He was a strict person. Whenever he came out, the kids would straighten right up and pay attention to him,'' said a neighbor who didn't want to be identified.

But friends were shocked by the allegations. "He was a very peaceful guy and a very smart person. And he was very religious," said the Rev. Wayne Lewis Jr., who attended Bible studies in the home. "The first time we met he was trying to convert me, but I am a Baptist minister.'"

The Slack home on South Brandon stood empty Monday, calm, with no traces of the tragedy. The family's two cars were parked outside in the 7900 block. Along the stairway to the second floor were a training manual for Jehovah's Witnesses, stapled sheets with math problems, a grill, a basketball hoop and a Domestic Violence Safety Plan issued by the Cook County state attorney's office.

The Slacks were a quiet family who stayed away from their neighbors, hidden behind a 6-foot-high wooden fence that Larry Slack built to replace a chain-link one.

Larry Slack, 42, is a 23-year employee of the CTA who was known as a "good machinist and a hard worker,'' Salabura said. Constance Slack, also 42, is believed to work at La Rabida Children's Hospital, he said.

Both parents have been charged with first-degree murder and also aggravated battery of a child for the alleged beating of their 8-year-old son, also on Saturday night.

The Slack's five other children all showed indications of physical abuse. They were taken into state custody and placed with relatives, authorities said. Larry Slack was treated at Advocate Christ Hospital and Medical Center Sunday night after allegedly attempting to kill himself while turning himself in to police at Area 2 detective headquarters. He was in the Central District lock-up Monday.

In a statement Monday, the Slack family said it was cooperating with police.

"We loved Laree dearly,'' said Leroy Slack, who identified himself as Larry Slack's uncle and a family spokesman. "We're very disturbed over the circumstances surrounding her death."

Contributing: Cathleen Falsani