Aaron Schaffhausen pleaded guilty to three counts of first-degree intentional homicide and one count of attempted arson in the July 10 deaths of his daughters, Amara, 11, Sophie, 8, and Cecelia, 5.
His lawyers maintained he was not legally responsible for the murders because he was insane at the time of the crime.
The jury unanimously concluded Tuesday that while Schaffhausen had a mental disease or defect at the time of the crime, he was legally sane during the incident, the St. Paul (Minn.) Pioneer Press reported.
Schaffhausen could be sentenced to a life in prison for each of the three counts of first-degree intentional homicide, the newspaper said.
Schaffhausen admitted he cut the throats of each of the girls in the River Falls, Wis., home they shared with their mother before attempting to set the house on fire.
Jessica Schaffhausen, the girls' mother, said she received a phone call while she was at work from Schaffhausen saying, "You can come now; I killed the kids."
Jessica's uncle, Flint Watt, said the family was pleased with Tuesday's verdict, and viewed it as "one step going forward in a long, long process to try to grieve and recover from this tragedy."
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