NAPERVILLE, Ill. » A suburban Chicago woman ordered her 7-year-old son and a kindergartner she was babysitting to kneel on a bedroom floor and pray, then stabbed them both dozens of times as they begged for their lives, striking again and again as she told her son he was going to heaven, authorities said today.

Officers who forced their way inside the locked apartment hours later found blood-spattered walls and the children’s bodies in a master bedroom where moments before the killings they had been happily jumping on a bed, prosecutors said.

The Naperville police chief said it was the most gruesome sight he’d seen in three decades on the job.

Elzbieta Plackowska, a 40-year-old immigrant from Poland, offered numerous explanations for the violence, including that she was battling the devil and trying to rid the children of evil, DuPage County State’s Attorney Robert Berlin said. But she eventually told investigators she stabbed the children and slashed their throats on Tuesday night because she was angry that her husband, a truck driver, was often away.

"She told the detectives that she thought by killing (her son) Justin she would make her husband hurt the way she hurt in their relationship," Berlin said.

Twenty-five miles west of Chicago, Naperville is known for its idyllic Riverwalk, bustling downtown shops and stellar schools. It’s also where Marilyn Lemak fed her three children peanut butter laced with antidepressants and suffocated them as revenge on her estranged husband 13 years ago.

Residents of the wealthy, usually quiet community struggled today to comprehend the latest bloodshed.

"I don’t understand anything that’s going on," said Tim Hooper, 28, who lives in the same condominium complex as the Plackowska family and would sometimes work out with an older son. "This is so out of the blue."

Plackowska told detectives she found Justin and 5-year-old Olivia Dworakowski jumping on a bed, Berlin said.

"She had grabbed the knife and she made both victims kneel and begin praying. She began stabbing her son Justin and told him he was going to heaven tonight. He pleaded for his life and told her to stop. But she continued stabbing him until he was dead," he said at a news conference after a judge ordered Plackowska held without bond.

"She then turned her attention to 5-year-old Olivia and began stabbing her with the knife multiple times. She, as well, pleaded for her life, but the defendant continued to stab her until she was deceased."

Plackowska killed Olivia because she had witnessed the attack on Justin, Berlin said.

The slayings took place at the home of Olivia’s mother, who works nights as a nurse and had left her daughter in Plackowska’s care before. Plackowska also stabbed the two family dogs.

Olivia’s body was found on the bed, and Justin’s was found on the floor beside it. He had stab wounds on his head, face, neck and back. Both appeared to have had their throats slit.

"In all my years in law enforcement, this is the most gruesome and horrific crime scene that I have seen," Naperville Police Chief Bob Marshall said at the news conference.

Investigators found two blood-stained knives; a steak knife in the kitchen sink and another in Plackowska’s car, Berlin said.

Still covered in blood and with scratches on her hands, Plackowska drove to a Catholic church. Finding it closed, she called the church and left a message saying she had "done something bad" and needed help, Berlin said. She then went to a friend’s home where her other, adult son was staying and said she had been robbed.

About the same time, Olivia’s mother, Marta Dworakowski, returned home to discover her door locked and the babysitter’s car gone. She called police to report her daughter was missing, and officers forced their way into the home.

Police took Plackowska into custody at her friend’s home, and prosecutors charged her with first-degree murder late Wednesday.

Plackowska initially told investigators that an intruder had broken into the home and killed the children while she was outside smoking a cigarette.

"She then changed her story and stated that she was really battling the devil … and that the children had evil inside them and she was trying to get the evil and devil out of them," Berlin said.

Later, she admitted she had lashed out in anger at her husband because he often left her alone to care for Justin and she worked as a cleaner, which she felt was beneath her, Berlin said.

In a brief telephone interview, Plackowska’s husband, Artur, denied the two were having problems.

"The day before (the killings) she told me that she loves me," he said.

However, a neighbor said he frequently heard the couple shouting at each other over the last five years.

"It happened once every other month," Victor Tuckenberry said.

There also were money troubles. Public records show the couple filed a Chapter 7 bankruptcy in 2009; a foreclosure in her name only was filed in 2007.

Still, Tuckenberry said Plackowska doted on her sons and he was shocked by the slayings. Plackowska and Justin "were together all the time," he said.

Plackowska arrived in the United States from her native Poland on a tourist visa 12 years ago, Berlin said. She is not a U.S. citizen and authorities were trying to verify her immigration status. Berlin said she has no prior history of violence, although she had a misdemeanor DUI from about 10 years ago.

Plackowska didn’t speak during today’s bond hearing other than to indicate she could not afford an attorney. The judge appointed a public defender.

Babwin reported from Chicago. AP News Researcher Jennifer Farrar contributed to this report from New York.