The judge in the trial of a man accused of murdering an abortion doctor dealt the defense a major setback Thursday, ruling that the jury cannot consider a lesser charge of manslaughter, the Associated Press reports.

The ruling came hours after Scott Roeder took the stand in his own defense and admitted killing Dr. George Tiller, saying he acted to save the lives of unborn children.

Roeder's attorneys had hoped to win a lesser conviction of voluntary manslaughter, which requires them to show their client had an unreasonable but honest belief that deadly force was justified. The charge carries a considerably lighter sentence than murder.

Roeder testified that he considered elaborate schemes to stop the doctor, including chopping off his hands, crashing a car into him or sneaking into his home to kill him.

But in the end, Roeder told jurors, the easiest way was to walk into Tiller's church, put a gun to the man's forehead and pull the trigger.

Testifying as the lone defense witness, Roeder calmly explained what he admitted publicly months ago — that he killed Tiller to save unborn children.

"Those children were in immediate danger if someone did not stop George Tiller," Roeder said as the jury watched attentively but without a hint of surprise.

"They were going to continue to die," he said. "The babies were going to continue to die."

Read the Associated Press story.