HUDSON, Wis. — Opening statements are expected to begin in the insanity trial of a man who admitted last week that he killed his three daughters in their River Falls home.

Thirty-five-year-old Aaron Schaffhausen pleaded guilty to three counts of first-degree intentional homicide, but he maintains he is not responsible because of a mental illness. Opening statements are scheduled to begin Tuesday morning in St. Croix County.

Prosecutors said Schaffhausen knew what he was doing last July when he killed 11-year-old Amara, 8-year-old Sophie and 5-year-old Cecilia. They said he did it because he was angry at his ex-wife.

If Schaffhausen is found 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 released someday.