HUDSON, Wis. — The mother of three girls who were killed by their father in northwestern Wisconsin told jurors Thursday that her ex-husband had previously threatened to kill the children as a way to hurt her.

Jessica Schaffhausen testified in St. Croix County Circuit Court that her ex-husband, Aaron Schaffhausen, harassed her with repeated phone calls after their divorce. She recalled one conversation on March 7, when he told her he “wanted to drive down there and tie me up and make me pick which child he killed and make me watch while he killed them.” She filed a police report after that incident.

On July 10, Aaron Schaffhausen called her and said: “You can come home now, I killed the kids.”

Aaron Schaffhausen pleaded guilty last week to killing 11-year-old Amara, 8-year-old Sophie and 5-year-old Cecelia, but maintains he is not responsible due to a mental illness. His trial, which began this week, is to determine whether he was sane at the time.

If Schaffhausen is found to be sane, he could go to prison for life. If the jury finds he was not responsible, he could be committed to a psychiatric institution and possibly could be released later.

Over her two days of testimony, Jessica Schaffhausen said she was afraid to leave her children alone with Aaron, and worried that he would forget to feed them or put them to bed on time.

She said her husband had stopped talking to the girls in October 2011 after moving to North Dakota for work, but that he would call her up to 30 times a day to harass her.

She said Aaron Schaffhausen called her the day of the murders to say he was in the area and wanted to see her and the kids. She said, “just the girls,” which made him upset and say “forget it.” But he called again later, and said he’d see the girls.

Jessica Schaffhausen testified that she allowed him to see his daughters because “they really missed him and wanted to see him … they loved him so much.”

She recalled on the stand that her ex-husband “called me and he told me that I could come home now because he had killed the kids. I started yelling at him that that wasn’t funny and he couldn’t say things like that.” She testified that Aaron Schaffhausen then hung up, and she immediately called police.

“I just wanted somebody to get there because they could have still been alive,” she said, and she began to cry.

Jessica Schaffhausen testified that when she first spoke with police, she described her ex-husband as “psychotic … truly irrational … crazy.” When asked about those words in court, she said she didn’t mean it as a mental diagnosis but rather in a “slang way.”