Wichita, Kan. - Before the first juror is selected or witness called, a decision allowing a confessed killer to argue he believes the slaying of one of the nation's few late-term abortion providers was a justified act aimed at saving unborn children has upended what most expected to be an open-and-shut case.

Abortion opponents are pleasantly stunned and eager to watch Scott Roeder tell a jury his slaying of Wichita doctor George Tiller was voluntary manslaughter. Tiller's colleagues and abortion rights advocates are outraged and fear the court's actions give a more than tacit approval to further acts of violence.

"This judge has basically announced a death sentence for all of us who help women," said Dr. Warren Hern of Boulder, Colo., a longtime friend of Tiller who also performs late-term abortions. "That is the effect of the ruling."

The facts of the case are not in dispute: On a balmy Sunday morning, Roeder got up from a pew at Wichita's Reformation Lutheran Church at the start of services and walked to the foyer, where Tiller and a fellow usher were chatting around a table. Wordlessly, he pressed the barrel of a .22-caliber handgun to Tiller's forehead and pulled the trigger.

Prosecutors charged Roeder with first-degree murder, and the 51-year-old from Kansas City, Mo., later admitted to reporters and in a court filing that he killed Tiller. The prosecution stands ready with more than 250 prospective witnesses to prove it.

But what had been expected to be a simple trial was altered Friday when Sedgwick County Judge Warren Wilbert decided he would allow Roeder to build a defense case calling for a lesser charge of voluntary manslaughter because he sincerely believed the May 31 slaying would save unborn children.

Kansas law defines voluntary manslaughter as "an unreasonable but honest belief that circumstances existed that justified deadly force." A conviction on that charge could bring a prison sentence closer to five years, instead of a life term for first-degree murder.

Prosecutors on Monday challenged the ruling, arguing that such a defense should not be considered because there is no evidence Tiller posed an imminent threat at the time of the killing.

"The State encourages this Court to not be the first to enable a defendant to justify premeditated murder because of an emotionally charged political belief," the prosecution wrote. "Such a ruling has far reaching consequences and would be contrary to Kansas law."

As events unfold inside a Wichita courtroom, the Kansas Supreme Court is considering a challenge from four media outlets, including The Associated Press, over the judge's decision to bar reporters from witnessing jury selection. A hearing is also scheduled for Tuesday afternoon to give the defense time to respond to Wilbert's decision to allow Roeder's voluntary manslaughter defense.

But key questions being asked outside the courtroom in the wake of Wilbert's decision have galvanized both sides of the abortion debate.

Will the judge's decision embolden militant anti-abortion activists and lead to open season on abortion providers? Does the Justice Department plan to file charges against Roeder under federal statutes guaranteeing access to clinics? And what does it portend for the unfolding case itself and the inevitable legal challenges to the nation's abortion laws?

Hern, of Boulder, Colo., said it's irrelevant that Wilbert won't decide until after the defense presents its evidence whether to allow jurors to actually consider a conviction on the lesser charge.

"The damage is done: The judge has agreed to give him a platform," Hern said. "It is an act of incomprehensible stupidity on the part of the judge, but he is carrying out the will of the people of Kansas who are trying to get out of the 19th century."

The Feminist Majority Foundation also denounced the ruling, saying Wilbert essentially was allowing a justifiable homicide defense. The group, which supports abortion rights, urged the Justice Department to file federal charges under the Freedom of Access to Clinic Entrances Act.

Justice Department spokesman Alejandro Miyar declined to comment, citing an ongoing investigation.

A man who runs a Web site supporting violence against abortion providers said in the wake of the judge's decision that he has changed his mind about attending Roeder's trial. The Rev. Don Spitz of Chesapeake, Va., said he and other activists from the Army of God plan to observe the court proceedings quietly next week.

"I am flabbergasted, but in a good way," Spitz said of the judge's decision.

Spitz acknowledged that the possibility that Wilbert's decision may influence some people who in the past wouldn't kill abortion providers because they risked a sentence of death or life imprisonment. "It may increase the number of people who may be willing to take that risk," he said.

In Des Moines, Iowa, militant anti-abortion activist Dave Leach agreed the decision opens the door to presenting the same evidence as in a case of justifiable homicide. It was Leach who wrote the 104-page legal brief that Roeder signed and submitted to the court in which he admitted killing Tiller.

"The closer we come to a court actually addressing these issues, the less danger abortionists are going to be in," Leach said.