The trial of the man accused of fatally shooting US late-term abortionist George Tiller began on Friday – the 37th anniversary of the Supreme Court’s controversial decision to legalise abortion in the country.

Lawyers were expected to begin making their cases to the jury of eight men and six women that will be deciding the fate of 51-year-old Scott Roeder. He has not denied shooting Tiller on May 31, 2009, as the abortion doctor was attending service at Reformation Lutheran Church in Wichita.

Prosecutors believe Roeder should be convicted of first-degree murder and be handed a life sentence.

The defence will be trying to build a case for a conviction on a lesser charge of voluntary manslaughter.

Roeder's lawyers want to argue that the Kansas City native believed Tiller's killing was necessary to save unborn children. As one of the few late-term abortion practitioners in the country, Tiller was regarded as among the most notorious figures in the pro-abortion movement and, at the time of his death, was under investigation by the Kansas State Board of Healing Arts for 11 petition allegations against him.

In a 30-minute phone interview last November, Roeder told The Associated Press that "defending innocent life" was what prompted him to shoot Tiller.

"It is pretty simple," he said.

In Kansas, voluntary manslaughter is defined as "an unreasonable but honest belief that circumstances existed that justified deadly force".

Under state sentencing guidelines, a conviction for voluntary manslaughter for someone with as little criminal history as Roeder would result in a sentence of around five years.

Despite the role that abortion issue played in the shooting and the timing of the trial, District Judge Warren Wilbert has repeatedly insisted that the trial would not turn into a debate over abortion.

Wilbert said he intends to keep the case as a "criminal, first-degree murder trial".