Updated

Opening statements in the murder trial of the man accused of shooting one of the nation's most prominent abortion providers began Friday on the 37th anniversary of the U.S. Supreme Court's landmark decision that legalized abortion.

Jurors will hear from witnesses who saw Dr. George Tiller gunned down at his church, listen to the emergency call made moments later, and see evidence of his blood on the accused killer's shoes, a prosecutor said.

LIVESHOTS: Opening Statements Under Way

Scott Roeder, 51, of Kansas City, Missouri, is accused of shooting Tiller, who specialized in late-term abortions. Roeder told The Associated Press in November that he killed Tiller to protect unborn children. Roeder also faces two charges of aggravated assault for allegedly threatening two church ushers who tried to stop him from fleeing. He has pleaded not guilty.

Before opening statements began, District Judge Warren Wilbert denied a defense motion to move the trial out of Wichita and a motion from prosecutors to not allow an involuntary manslaughter defense.

Wilbert has repeatedly said the trial will not turn into a debate over abortion, warning Roeder's lawyers that he intends to keep the case as a "criminal, first-degree murder trial."

But the judge galvanized both sides of the abortion battle when he refused, on the eve of jury selection, to block the defense from trying to build a case for a conviction on a lesser charge of voluntary manslaughter.

The defense wants to argue that Roeder believed Tiller's killing was necessary to save unborn children. In Kansas, voluntary manslaughter is defined as "an unreasonable but honest belief that circumstances existed that justified deadly force."

If convicted of first-degree murder, Roeder faces a life sentence. Under state sentencing guidelines, a conviction for voluntary manslaughter for someone with as little criminal history as he has would bring a sentence closer to five years.

The opening arguments coincided with Friday's anniversary of the U.S. Supreme Court's 1973 Roe v. Wade decision that legalized abortion.

Church members were gathering the morning of May 31 in the fellowship hall, where Tiller was scheduled to serve as an usher, Sedgwick County District Attorney Nola Foulston told the jury of eight men and six women.

"Then unexpectedly, a sound was heard, like a popping of a balloon," she said.

Foulston said a witness saw "a man standing next to George Tiller with his arm still raised and ... Dr. Tiller fell to the floor. ... And the assailant was running."

Jurors will hear several witness accounts of Tiller's shooting, she said, and other evidence will include Roeder's shoes with Tiller's blood on them and a police video of Roeder's arrest later that day.

Jury selection in the case occurred for the most part behind closed doors. After six days of secret questioning of potential jurors, the court finally opened jury selection to the media on Thursday while turning away public spectators.

Tiller, whose Wichita clinic closed after his death, championed abortion rights even after being shot in both arms by an activist in 1993. The clinic, heavily fortified after a bombing in 1986, was the target of both peaceful and violent protests. In 1991, a 45-day "Summer of Mercy" campaign organized by Operation Rescue drew thousands of anti-abortion protesters to Wichita for demonstrations and saw mass arrests.

In more recent years, anti-abortion activists had focused their attacks against Tiller within the legal system and political arena. Thousands of abortion opponents signed petitions forcing Sedgwick County to convene grand juries in 2006 and 2008 to investigate him, but both refused to indict him.

Two state attorneys general in Kansas also tried in vain to prosecute him. Just two months before his death, a jury acquitted Tiller of misdemeanor charges accusing him of failing to get an independent second opinion for late-term abortions. The state's medical board was investigating similar allegations at the time of his killing.