Marilyn Lemak called the Naperville police herself. The house on Loomis Street was a cranberry-red Victorian built in 1885, in the city's historic district, a block from neighbors who later said nothing had ever seemed wrong there. Officers found Nicholas, seven, and Thomas, three, dead in their beds. Emily, six, lay in her parents' bedroom, and her mother was beside her. Lemak had swallowed pills and cut her arm, and she survived. The killings are dated March 4, 1999, a Thursday; the first newspaper reports had the police arriving on the Friday.
Prosecutors said she had given the children a mix of aspirin derivatives and prescription drugs to make them drowsy, and when they were asleep had suffocated them one at a time, pinching each child's nose and holding a hand over the mouth. She was forty-one, a former surgical nurse, thirteen years married to David Lemak and in the middle of divorcing him.
To the neighborhood she was Lynn, a woman who waved while she jogged and walked her children to Ellsworth School, and who the summer before had worked a lemonade stand with them. "She was the basic Naperville woman," a neighbor, Shannon Watson, told the Chicago Tribune. "She was a very nice, very outgoing, very friendly person who loved her kids." Watson remembered her holding Emily in her lap and calling her Angel Baby. On the Monday night before the killings the two women had settled a kitchenware order, a vegetable peeler, an apple corer, two oven mitts, an oil spritzer and two soap dispensers, eighty dollars in all, and Lemak had talked about hosting another party at the house.
The children were buried after a funeral on March 11 at Ss. Peter and Paul Church. Their father described them three years later, in court, introducing each one with the same words, "Let me tell you a little bit about." Nicholas was a good student who loved to learn and to dress up as a policeman or a secret agent. Emily was a budding artist. Thomas was "the happiest child I've known." "His greatest thrill, I think, was every day," he said. A CBS report on the twentieth anniversary gave Emily's age as seven; the contemporary reports and her father's statement give six.
DuPage County State's Attorney Joseph Birkett announced that he would seek the death penalty, and the defense gave notice that it would plead insanity. The case produced a ruling of its own before trial. Lemak's lawyers asked to depose David Lemak under a new Illinois Supreme Court rule, Rule 416(e), which allowed depositions in capital cases, and Circuit Judge George Bakalis agreed. Birkett asked the Supreme Court to overturn the order. On June 21, 2001, in People ex rel. Birkett v. Bakalis, the court declined to intervene, finding that the rule applied and that the judge had not abused his discretion. Justice Thomas dissented, arguing that a grieving father was not the kind of witness the rule was written for and that the order bore on the rights of crime victims.
The trial ran three weeks in December 2001. Lemak did not dispute that she had killed her children. Her lawyers, led by John Donahue, described a woman seriously depressed who had lost her sanity as her marriage came apart and who had killed the children and tried to kill herself believing they would all be reunited in a better place. The prosecution's case was that she had acted out of anger after her husband began seeing someone else. David Lemak's second wife, Janice, was allowed to testify about harassing phone calls that prosecutors attributed to Marilyn Lemak in the weeks before the killings. The jury deliberated for about nine hours over two days, found that she had been sane, and convicted her of three counts of first-degree murder. One juror, Allan Munch, said years later that the jurors had searched for an explanation and never found one.
In January 2002 prosecutors decided not to pursue a death sentence, which left the judge a single option under Illinois law, natural life. At a thirty-minute hearing in the Wheaton courthouse on April 8, 2002, Bakalis first rejected a motion for a new trial that listed seventeen alleged errors: that the state's insanity statute was unconstitutional, that Janice Lemak should not have testified, and that a juror who told the Tribune after the verdict that he "thought [Lemak] was guilty from the beginning" should be questioned. He refused to question the juror.
David Lemak then took the stand. "I miss their smell after bath time and when they snuggled up with me on the couch," he said. "I regret that I'll not see them off on their first dates or their weddings." He asked for the sentence the law already required, saying that his family believed the fitting punishment was for Marilyn Morrissey, as he called her, to spend the rest of her life in prison, where "she cannot harm any of us ever again." Bakalis, a judge known in the courthouse for his reserve, told her that every day, looking at the walls and the bars, she would see the children's faces and hear them asking, "Why, Mom? We loved you, Mom. Why did you do this to us?" He sentenced her to life without the possibility of parole and ordered psychiatric care "so you will always maintain the capacity to understand the horror of your crime." On her lawyers' advice she said nothing. Birkett called it the sentence "she richly deserves." Donahue promised an appeal.
She was taken to Dwight Correctional Center. Ten years after the killings Donahue told the Daily Herald that she was medicated, surviving, and using her nursing training to help other prisoners. Her only interview after her conviction went to the French television channel M6 in 2012, and in it she blamed the killings on her depression and her divorce. By the twentieth anniversary she had been moved to Logan Correctional Center in Lincoln. The house on Loomis Street was given to North Central College in 2008, as part of a four-million-dollar gift from a Naperville couple.