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Prosecutors say the mother of a 5-year-old girl stabbed to death this week would have had no hint that something might be wrong when she left her daughter with the babysitter now accused of killing the girl and the woman's own 7-year-old son.

Elzbieta Plackowska had watched the suburban Chicago kindergartner fairly regularly since the beginning of the school year, DuPage County State's Attorney Robert Berlin said. As far as prosecutors know, Plackowska has no history of mental illness or hospitalizations. And the investigation has turned up nothing that might have given the girl's mother pause about letting her continue babysitting, he said.

"There was really no indication," Berlin said. "Nothing."

The kindergartner's mother, Marta Dworakowski, could not be reached for comment Friday. Reached by phone on Thursday, she told the Chicago Tribune, "I'm not ready to talk to anyone yet."

Investigators continued Friday to interview people close to Plackowska and to comb the car she was driving Tuesday night for evidence. Berlin has said that a bloody knife — one of two believed to have been used in the killings — was found inside the vehicle. On Friday, a judge signed an order giving prosecutors possession of the car once police are finished with it.

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Plackowska, a 40-year-old Polish immigrant, came to the United States 12 years ago on a tourist visa, Berlin said. The U.S. Immigration and Customs Enforcement said Friday it had placed a hold on her because she could be eligible for deportation. ICE officials did not elaborate on the agency's statement, but one common reason ICE starts deportation proceedings is because someone's tourist visa has expired.

For now, Plackowska is being held without bail in the DuPage County jail. She has been charged with first-degree murder in the children's deaths. Authorities say she stabbed them dozens of times as they begged for their lives.

Berlin said previously that Plackowska told investigators she killed her son because she was upset with her husband and the girl because she was a witness. On Friday, he said Plackowska told authorities she had been upset about her own father's recent death, but he couldn't say what role, if any, her grief may have played in her actions Tuesday.

The children's gruesome deaths have shaken Naperville, a vibrant, populous suburb 25 miles west of Chicago. Officers discovered their bodies after Dworakowski reported her 5-year-old daughter, Olivia, missing. Dworakowski had arrived home to discover her door locked and the babysitter's car gone. Police found Olivia on a bed and 7-year-old Justin Plackowska on the floor beside it.

Plackowska told investigators that the children had been jumping on the bed. She ordered them to kneel on the floor and pray and then stabbed them both dozens of times as they begged for their lives, Berlin said.

Covered in blood, Plackowska drove to a Catholic church. Berlin said Friday that it was the same one where she went to confession before the slayings.

Finding the building 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 adult son was staying. Police arrested her there.

Berlin said Plackowska had been babysitting for Dworakowski since the beginning of the school year, although Justin and Olivia went to different schools and it wasn't clear how or when the two women met. Plackowska babysat Olivia numerous times as her mother works various shifts as a nurse, he said.

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