Judge Wilbert ruled that he would not instruct the jury to consider a lesser charge when they begin deliberations on Friday. Mr. Roeder has pleaded not guilty to murder, but defense lawyers had argued that his beliefs about abortion might warrant a voluntary manslaughter conviction if jurors concluded that Mr. Roeder possessed, as Kansas law defines it, “an unreasonable but honest belief that circumstances existed that justified deadly force.”

Image Scott Roeder testifying at his murder trial in Wichita, Kan., on Thursday. Credit... Pool photograph by Jeff Tuttle

Seated on the witness stand, facing a tiny courtroom gallery that included Dr. Tiller’s widow, Jeanne, abortion opponents from other parts of the country, and national abortion rights supporters, Mr. Roeder seemed quiet, almost lawyerly, in his responses to inquiries about the killing, in which Dr. Tiller was shot in the forehead, the gun pressed to his skin.

Mr. Roeder, 51, of Kansas City, Mo., told jurors that he had a growing sense of his own faith and opposition to abortion in the 1990s after watching “The 700 Club,” the evangelist Pat Robertson’s television talk show. Mr. Roeder’s views on religion and abortion, he said, went “hand in hand.”

Mr. Roeder acknowledged under cross-examination that he had, as early as 1993, thought about killing Dr. Tiller. A year before the shooting, he said, he had gone to Dr. Tiller’s church with a gun intending to shoot him. (Dr. Tiller was not there that day, he said.) And he said he considered other alternatives: cutting off Dr. Tiller’s hands with a sword, shooting him from a distance with a rifle, or finding him at his house.

Of his decision to go to the church, he said, “It was the only window of opportunity I saw that he could be stopped.”

Abortion opponents here, including some who have served time in jail for abortion clinic violence, praised Mr. Roeder for his testimony. But some complained bitterly that Judge Wilbert had severely limited the defense by barring the testimony of Phill Kline, a former Kansas attorney general who had unsuccessfully pursued criminal investigations against Dr. Tiller and by preventing jurors from considering some conviction short of murder.