A federal judge began vetting would-be jurors Monday in the death-penalty trial of a former University of Illinois physics student charged with kidnapping, torturing and killing a visiting Chinese scholar.

Brendt Christensen, 29, looked on in a dress shirt from a defense table as the judge put initial questions to jurors. If a jury ends up convicting him for killing 26-year-old Yingying Zhang — who aspired to become a professor to help out her working-class family in China — the trial would then enter a death-penalty phase.

When Judge James Shadid asked one potential juror Monday why she was against executions, she replied: "God doesn't want us to take revenge," Champaign's News-Gazette reported.

Those who categorically oppose capital punishment or who believe it should be imposed on someone convicted of killing without expectation can't serve as jurors in federal death-penalty cases. They'll be dismissed.

Zhang's parents were among those at the central Illinois courthouse in Peoria. The father was in court, while the mother was in an overflow room, the News-Gazette reported. They traveled from China last week and were initially expected to watch remotely from a closed-circuit video at a courthouse near the university's Champaign campus.

Zhang's mother, Lifeng Ye, told ABC News in a recent interview about her reaction when she heard of Christensen's arrest, saying, "I wanted to kill him at the time."

"I cannot believe there is such an evil person among us in this world." Zhang's father, Ronggao Zhang, added. "I think he should definitely get the death penalty."

Zhang disappeared June 9, 2017, as she ran late to sign an apartment lease off campus in Urbana, 140 miles (225 kilometers) southwest of Chicago. She'd just missed a bus when Christensen lured her into his car, prosecutors say. He was arrested June 30, his birthday, and pleaded not guilty to kidnapping resulting in death.

Prosecutors haven't offered details about how they think Christensen killed Zhang, but they offered clues last week in an exhibits list that includes a baseball bat and apparent blood stains in Christensen's apartment.

The trial was moved to Peoria out of concern that intense feelings about the case in the Champaign-Urbana area could make it harder to pick a jury that could give Christensen a fair trial.

Other potential jurors Monday said they agreed with the death penalty in principle but said they may feel uncomfortable about having the power to apply it. Nearly all those questioned had previously heard about the case.

Illinois abolished capital punishment in 2011, but it is available under federal law.

Twelve jurors and six alternates are being selected from an initial jury pool of more than 400, with Shadid saying he hoped to question 32 each day. Seventy vetted potential jurors will be chosen this week, and next week — before opening statements — the defense and prosecution can each dismiss any 20 without giving a reason.

Complicating the task of prosecutors is that Zhang's body hasn't been found. They'll point to Zhang's blood and that a cadaver-sniffing dog indicated a dead body had been in Christensen's apartment that she's dead.

Zhang's mother told ABC News she now hopes to learn Christensen didn't take her daughter's life.

"I hope he would give my daughter back to me," she said.

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