Wichita ? Defense attorneys have “a formidable and daunting task” ahead if the man who has confessed to killing a Kansas abortion provider is hoping for a chance at a lesser sentence by arguing he sincerely believed his actions were necessary to save unborn children, a judge said Wednesday.

Scott Roeder will take the witness stand to testify on his own behalf, attorney Steve Osburn told The Associated Press in the wake of a heated hearing about which defense evidence jurors will be allowed to hear.

Osburn said the defense expects to present its case in a single day today.

Roeder, 51, is charged with premeditated, first-degree murder in the May 31 shooting of Dr. George Tiller, one of the nation’s few late-term abortion providers. The Kansas City, Mo., man also was charged with two counts of aggravated assault for allegedly using a gun to threaten two ushers who tried to stop him.

Attorney Mark Rudy confirmed to the court for the first time Wednesday that the defense would build a case based on the lesser charge of voluntary manslaughter — defined in Kansas as “an unreasonable but honest belief that circumstances existed that justified deadly force.”

A voluntary manslaughter conviction for someone with little criminal history carries a sentence of about five years, compared to the life sentence Roeder faces if convicted of first-degree murder.

District Judge Warren Wilbert reminded attorneys they must couple a voluntary manslaughter defense with a showing of imminent danger posed by the doctor. Wilbert will rule at the end of the defense’s case whether there is sufficient evidence to instruct jurors that they can consider the lesser charge.