Charleston - Twelve jurors were chosen on Wednesday to decide the death penalty trial of a white man who authorities say wanted to start a race war by killing nine black people in a South Carolina church.Opening statements were underway in the trial of Dylann Roof in a federal courthouse about a mile away from the church. Roof wore a grey and white striped prison jumpsuit and stared mostly at the table in front of him.According to a reporter who observed the jury selection process, the panel appears to be racially mixed.Authorities say Roof sat with 12 people in Bible study and prayer for an hour at Emanuel African Methodist Episcopal Church on June 17, 2015, before pulling a gun from his fanny pack, firing dozens of shots and reloading several times.His trial begins as another racially charged one ended on Monday in a mistrial. Jurors couldn't agree on a verdict for former North Charleston police officer Michael Slager, who shot a black man in the back as he was running away from a traffic stop.In contrast to the Slager case, Roof's lawyers have offered several times to plead guilty if federal prosecutors agreed not to seek the death penalty. They refused.Authorities say Roof hurled racial insults during the massacre, telling the parishioners he was killing them because he wanted a war between whites and blacks because blacks were raping white women and taking over the country.Roof left three people alive in the church basement so they could tell the world his reasons for the shooting, police said. Two others, who were in another room, also survived.The church slayings took place a little more than two months after the Slager shooting, which was shown online and on TV millions of times after a bystander recorded it. Charleston has stayed mostly calm, and the State prosecutor has promised a retrial.Prosecutors have said it would take six to seven days to make their case against Roof. Defence attorney David Bruck said Roof's case would take little additional time.The past week has had its own drama as Roof fired his lawyers to act as his own attorney, then hired them back on Monday. But he said he will represent himself if he is found guilty and must fight for his life during the penalty phase.Roof's attorneys said they don't know why he wants to be his own lawyer, but said in other cases defendants have been trying to avoid having their lawyers introduce embarrassing evidence that could sway jurors.Roof faces 33 charges, including hate crimes and obstruction of religion. State prosecutors also plan a death penalty trial on nine murder charges.