Olathe ? Attorneys representing a man charged with killing his social worker with a chain saw will not use their client’s mental illness as a defense.

As jury selection got under way Monday in the trial of Andrew Ellmaker, Judge Peter V. Ruddick agreed to a defense request to no longer offer evidence of Ellmaker’s mental state at trial. Ellmaker’s attorneys filed a motion asking to drop the defense Friday in Johnson County District Court.

Ellmaker, 20, is charged with first-degree murder in the August 2004 death of Teri Lea Zenner, 26, who worked for the Johnson County Mental Health Center. She was killed when she went to Ellmaker’s Overland Park home after telling her husband she had to make sure a client was taking his medication.

When police arrived at Ellmaker’s house, court documents said he freely told officers, “I just killed my therapist with a chain saw.”

Ellmaker also is charged with aggravated battery for injuries his mother suffered.

Opening arguments are expected Wednesday, and the state’s case is expected to take two days.

“Our case will be substantially shorter because we don’t have to bring on witnesses to counter that (mental illness) defense,” said Brian Burgess, spokesman for Johnson County District Attorney Phill Kline.

A message for defense attorney Jessica Glendening was not immediately returned Monday.

Ellmaker’s previous attorneys initially claimed their client’s mental state did not allow him to understand or intelligently waive his Miranda rights. Among other things, the defense had said Ellmaker took 60 pills, including Lithium, Nyquil and Seroquel, in an attempt to kill himself.

But an emergency room doctor testified during a July 2006 hearing that Ellmaker was “very clearly oriented” shortly after the attack.