The man charged with killing his three daughters in River Falls, Wis., last year entered an insanity plea on Wednesday, and the legal wrangling threatens to delay the planned start of the trial in April.

The plea was entered on behalf of Aaron Schaffhausen in a one-paragraph letter from his attorney, John A. Kucinski, an assistant public defender in Wisconsin. A Dec. 14 deadline for an insanity plea had been set by the judge; the prosecutor had expressed concern that a psychological exam needed in such cases could take up to three months.

The plea sets up a two-phase trial, the first to determine whether Schaffhausen committed the crimes, then one to ascertain his state of mind and determine whether he's not guilty by reason of insanity.

Calls to Kucinski seeking further comment were not returned Wednesday. Dana Brueck, a spokeswoman for the Wisconsin Department of Justice, which is helping in the case as a special prosecutor, said the agency had no comment on the plea.

Schaffhausen, 35, was charged July 12 with three counts of first-degree intentional homicide in the deaths of his daughters Amara, 11; Sophie, 8, and Cecilia, 5. He had shared legal custody of the girls with their mother, Jessica Schaffhausen, his former wife.

In court appearances so far, he has sat still and silent. When Schaffhausen was asked at an August hearing how he pleaded to charges against him, Kucinski answered for him, saying they opted to "stand mute." The court, by law, then entered a plea of not guilty.

The insanity plea can be withdrawn at any time before trial. Should that happen, any psychological evaluations performed in support of the plea would not be admissible.

When the deadline set by St. Croix County Circuit Judge Howard Cameron passed in December, Kucinski said he was not pursuing an insanity defense "as of now."

A hearing on a variety of motions before Cameron is scheduled for 8:30 a.m. Thursday in the Circuit Court in Hudson, Wis. Among the issues that are expected to be discussed or ruled upon are changing the venue for the trial, the admissibility of statements Schaffhausen made to police and whether to allow cameras in the court.

The insanity plea says Schaffhausen is pleading not guilty "by reason of mental disease and defect to all four counts" -- three counts of first-degree intentional homicide and one of attempted arson. Authorities at the crime scene found a gas fireplace turned on and gasoline poured in the basement.

Schaffhausen faces the possibility of life in prison on each intentional homicide charge if he is convicted.

According to a criminal complaint, Schaffhausen, then a carpenter living in Minot, N.D., called and texted his ex-wife around noon on July 10, saying he was nearby and asking to spend time with the children.

She agreed but told him he had to leave the house by 3:30 p.m., before she got home, the complaint says. A baby sitter said the girls were excited to see him and led him upstairs to show him their things.

The sitter left, and at 3:30, Jessica Schaffhausen told police, she got a call from her ex-husband telling her he had killed the children. Authorities found them in their beds. Two had died after having their throats slit; the third girl was strangled and had cuts on her neck.

Heron Marquez • 952-746-3281