Elzbieta Plackowska had "a psychotic belief" that the devil was inside her son and a young girl when she stabbed them to death nearly five years ago, a forensic psychiatrist testified Wednesday.
The Naperville woman believed that killing the children was the right thing to do.
Defense psychiatrist Phillip Resnick says Plackowska thought she was "killing the devil" and letting 7-year-old Justin Plackowski and 5-year-old Olivia Dworakowski go to heaven. "She believed God approved of what she was doing," Resnick said.
Resnick's testimony came during the seventh day of Plackowska's double-murder trial.
Prosecutors say Plackowska killed the children while baby-sitting at Olivia's Naperville home. The 45-year-old woman also is accused of fatally stabbing her dog and Olivia's dog.
Plackowska told investigators that she killed her son to get back at her husband, a trucker who spent most days traveling away from home. Prosecutors say her murderous rage was fueled by alcoholism and a feeling of worthlessness.
But defense attorneys say Plackowska started losing her battle with bipolar disease in the weeks after her father's death. They say she wasn't in control of her actions Oct. 30, 2012, when she repeatedly stabbed Justin and Olivia.
Resnick, who is an expert on parents who kill their kids, testified that Plackowska became psychotic several days before killing Justin and Olivia.
During that time, Plackowska claimed that she saw the devil in Justin. She forced the young boy to watch religious movies "to counteract the devil," according to Resnick.
Resnick said Plackowska was out of touch with reality and experiencing delusions on the night of the deaths.
On Oct. 30, Plackowska picked up Justin and Olivia as she normally would. But instead of going straight to Olivia's home, she took the children to church in Naperville.
She eventually took them to Olivia's home and let the children play for a bit before getting them ready for bed.
Plackowska claimed that he was with the children a master bedroom when she saw "a black shadow" appear and enter the children. She thought the devil was taking control of the kids, Resnick said.
After telling the children to kneel and pray, Plackowska got a knife and killed Justin. She then turned the knife on Olivia.
Plackowska later said that something took control of her, according to Resnick. He said Plackowska killed the dogs because she didn't want them to be left behind.
Despite thinking the kids went to heaven, Resnick said, Plackowska had doubts about what she did.
Plackowska traveled to a friend's house in Naperville. While en route, she called her church and left a message saying she "saw the devil" and "did something wrong."
At the friend's house, Plackowska lied and said an intruder killed the kids. Someone at the house called police.
Around the same time, Olivia's mother, who had been at work, was calling police because she was locked out of her townhouse and couldn't find Plackowska or her child.
Naperville officers forced entry into the townhouse to find blood covering a hall leading to the master bedroom. Investigators found a blood-soaked steak knife in the kitchen sink and another bloody knife in Plackowska's car.
The children were in the bedroom -- Justin on the floor and Olivia on the bed.
When she was taken to the jail Oct. 31, Plackowska was agitated, uncooperative and talked rapidly. She also was laughing uncontrollably.
A jail psychiatrist says Plackowska thought someone was after her or trying to control her. She also claimed her food had been poisoned.
Her bizarre behavior continued for several weeks. But Resnick says Plackowska started to improve on Nov. 5.
He said he doesn't believe Plackowska was pretending to be mentally ill.
"She was not malingering," or fabricating signs of mental illness, Resnick said. "She was genuinely psychotic for eight days."
Prosecutors are scheduled to cross-examine Resnick on Thursday.