Defense attorney Mark Rudy said the case was virtually hopeless after Roeder took the stand and confessed.
"I've never seen anyone lay himself out as much as Mr. Roeder did," Rudy said after the verdict.
Roeder's frankness did not win him the possibility of lighter sentence as he had hoped. Instead, it prompted a swift reaction from the trial judge who told the jury they would not be allowed to consider a lesser charge of manslaughter.
In Kansas, a murder charge can be downgraded to manslaughter if the defense can prove the suspect had an unreasonable yet honest belief that killing another person was justified.
"If I didn't do it, those babies would die the next day," Roeder testified, describing how he shot and killed Tiller in a church vestibule.
Roeder's testimony, gruesome at times, proved immensely difficult for Tiller's family, who openly cried in court. He detailed how he walked up to Tiller at the Reform Lutheran Church, put a gun to the doctor's head and pulled the trigger.
He told the jury of how his religious faith had convinced him that what Tiller was doing was wrong and how he had considered cutting off the doctor's hands with a sword. When told Tiller's clinic had closed and asked if he felt regret, Roeder replied simply, "No I don't."
The Associated Press contributed to this report