NAPERVILLE, Illinois -- The attorney for a suburban Chicago woman accused of stabbing to death her young son and a girl she was babysitting asked the public not to rush to judgment after the woman's arraignment hearing on Wednesday.

Elzbieta Plackowska pleaded not guilty to first-degree murder in each child's death. Prosecutors allege she stabbed her 7-year-old son more than 100 times because she was angry with her husband, and then stabbed the 5-year-old girl about 50 times because she was a witness.

Prosecutors said Wednesday that a psychiatrist has started a mental health evaluation of Plackowska in anticipation she may use an insanity defense. They said the process could take months.

Outside a DuPage Country courthouse after a brief hearing, public defender Michael Mara told reporters he will start building Plackowska's defense after the prosecution turned over photographs and 40 CDs and DVDs from its investigation. The county's top prosecutor, DuPage County State's Attorney Robert Berlin, says the material includes Plackowska's confession.

"What happened here is a tragedy but it's important to remember not to rush to judgement," Mara told reporters. "Now we can start our defense."

Plackowska's next court appearance is scheduled for Jan. 4.

During the hearing, she stood silently in a blue jail uniform beside Mara. The hearing was broadcast live on websites as part of Illinois' experiment with using cameras in courtrooms for the first time.

Plackowska has told investigators that the children had been jumping on the bed at the girl's home in Naperville. She ordered them to pray, then stabbed them both dozens of times as they begged for their lives.

The 40-year-old Polish immigrant told investigators she killed her son, Justin, because she was upset with her husband, a truck driver who was often away from home. Prosecutors say she killed the girl, Olivia Dworakowski, because she had witnessed her son's death.

Berlin says 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 families met. Plackowska babysat Olivia numerous times as her mother works various shifts as a nurse, he said.

Earlier on HuffPost:

Loading Slideshow...
  • Justin Plackowska, 7, and Olivia Dworakowski, 5, were found stabbed to death in his home in Naperville, Tuesday night, Oct. 30.

  • Elzbieta Plackowska, Mike Mara, Robert Kleeman, Bob Berlin, Adam Kleczyngier,

    From left, DuPage State's Attorney Robert Berlin, Senior Assistant Public Defender Mike Mara, Elzbieta Plackowska, a DuPage County sheriff's deputy and interpreter Adam Kleczyngier, appear before DuPage County Judge Robert Kleeman, rear, during Plackowska's arraignment Wednesday, Nov. 21, 2011 in Wheaton, Ill. Plackowska is charged with fatally stabbing her seven year old son and a five year-old girl she was babysitting. (AP Photo/M. Spencer Green, Pool)

  • Elzbieta Plackowska, who is charged with fatally stabbing her 7-year-old son and a 5-year-old girl she was babysitting, appears before DuPage County Judge Robert Kleeman during her arraignment November 21, 2012 in Wheaton, Illinois. Plackowska is charged with fatally stabbing her 7-year-old son and a 5-year-old girl she was babysitting. Plackowska appeared in court in a blue jail uniform and stood silently beside her public defender as he entered the not guilty pleas on her behalf during the brief hearing before Judge Robert Kleeman. (Photo by M. Spencer Green-Pool/Getty Images)

  • Elzbieta Plackowska, right, who is charged with fatally stabbing her seven year old son and a five year-old girl she was babysitting is seen in court during her arraignment Wednesday, Nov. 21, 2011 in Wheaton, Ill. Plackowska appeared in court in a blue jail uniform and stood silently beside her public defender as he entered the not guilty pleas on her behalf .(AP Photo/M. Spencer Green, Pool)

  • From left, Elzbieta Plackowska, DuPage State's Attorney Robert Berlin, and Senior Assistant Public Defender Mike Mara appear before DuPage County Judge Robert Kleeman during Plackowska's arraignment Wednesday, Nov. 21, 2011 in Wheaton, Ill. Plackowska is charged with fatally stabbing her seven year old son and a five year-old girl she was babysitting. (AP Photo/M. Spencer Green, Pool)

  • A makeshift memorial is seen outside a home in Naperville, Ill., Thursday, Nov. 1, 2012, where two children were found stabbed to death on Tuesday, Oct. 30. Elzbieta Plackowska was accused Thursday of stabbing her 7-year-old son 100 times and a 5-year-old girl she was babysitting about 50 times. (AP Photo/M. Spencer Green)

  • Police cars are seen outside a home in Naperville, Ill., Thursday, Nov. 1, 2012, where two children were founded stabbed to death on Tuesday, Oct. 30. Elzbieta Plackowska, 40, was charged with first-degree murder and denied bond at a hearing Thursday in Wheaton, Ill. Prosecutiors said Thursday that Plackowska stabbed her 7-year-old son 100 times because she was angry with her husband and a 5-year-old girl about 50 times because she witnessed the attack, as both children prayed and begged for their lives. (AP Photo/M. Spencer Green)

  • Elzbieta Plackowska

    This Thursday, Nov. 1, 2012 booking photo provided by the DuPage County Sheriff's Department in Wheaton, Ill., shows Elzbieta Plackowska, 40, of Naperville, Ill., who was charged with first-degree murder in the deaths of her 7-year-old son and a 5-year-old girl. Prosecutors contend that on Tuesday, Oct. 30, 2012, Plackowska stabbed her son because she was angry with her husband and killed the 5-year-old girl she was babysitting because she witnessed the attack. Plakowska was ordered held without bond at a hearing Thursday in Wheaton. (AP Photo/DuPage County Sheriff's Department)


***