Updated 5:15 p.m.
The man accused of killing Kansas late-term abortion provider George Tiller has pleaded not guilty.
Authorities say anti-abortion activist Scott Roeder, 51, also threatened two ushers who tried to stop him during the May 31 shooting in the doctor's church in Wichita. Roeder is charged with first-degree murder and aggravated assault in the slaying.
He pleaded not guilty to all charges on Tuesday after witnesses gave chilling testimony at a preliminary hearing. A judge ordered Roeder held on $20 million bond and set a trial date for Sept. 21.
Tiller was the target of protests at his Wichita clinic. He practiced as one of the nation's few providers of late-term abortions and was shot in both arms by an anti-abortion activist in 1993.
Gary Hoepner, an usher at Reformation Lutheran Church, was the first witness called Tuesday in the preliminary hearing. Hoepner said he and Tiller were making small talk when he saw a man come in a door, put a gun to Tiller's head and shoot him.
An emotional Hoepner said, "I wasn't sure if it was a cap gun or what. And then George fell to the ground and I just said in my mind 'oh my God."
He said he followed the shooter, who he identified as Roeder, out of the church but stopped after Roeder warned him.
"'I've got a gun and I'll shoot you,"' Hoepner recalled Roeder saying. "I believed him and I stopped."
Hoepner tried not to think about his testimony before Tuesday's hearing.
"I've tried to put it out of my mind as much as possible because I know I'm going to have to relive it," Hoepner told CBS News Kansas affiliate KWCH.
Prosecutors have to convince Sedgwick County District Judge Warren Wilbert they have enough evidence to merit a trial.
Tiller, 67, had been the target of regular protests for most of the 36 years he performed abortions at his Wichita clinic, where he practiced as one of the nation's few providers of late-term abortions. He was shot in both arms by an anti-abortion activist in 1993, and the doctor had been repeatedly threatened over the years.
It is unknown how many people the prosecution might call for Tuesday's hearing, but the witness list has 220 names, mostly law enforcement officials.
Also on the list are members of the anti-abortion group Operation Rescue; Roeder's ex-wife and son; Tiller's wife, Jeanne, who was singing in the choir when her husband was shot; and Rachelle "Shelley" Shannon, who shot Tiller in 1993.
In rambling jailhouse interviews, Roeder has talked about the notion of justifiable homicide against abortion providers, but he has refused to discuss any facts of his case.
Roeder has told The Associated Press Tiller's shooting was justified, but never has claimed a role in the slaying.
If Roeder is convicted of first-degree murder, he faces life in prison with the possibility of parole after 25 years.