HUDSON, Wis. (AP) -

A prosecutor says a Wisconsin man on trial for killing his three young daughters in July was driven by revenge against his ex-wife.

Gary Freyberg, Wisconsin's assistant attorney general, told jurors Tuesday that Aaron Schaffhausen decided killing the girls was the best way to punish his ex-wife.

The 35-year-old Schaffhausen has admitted killing his daughters -- ages 11, 8 and 5 -- at their home in River Falls, Wis., last July. Schaffhausen is seeking to convince a jury he's not responsible due to mental illness.

Freyberg used his opening statement to reject the idea that Schaffhausen couldn't control his emotions or actions.

Freyberg says Schaffhausen planned the killings, brought the tool he used to cut his daughters' throats with him from North Dakota and tried to get rid of evidence.