A federal jury sentenced the former University of Illinois physics doctoral student who kidnapped and murdered a visiting Chinese scholar to life in prison on Thursday.

Brendt Christensen, 29, was found guilty last month during his trial at the U.S. District Court in Peoria, after his own defense team admitted that he was responsible for 26-year-old Yingying Zhang’s death.

Though Illinois no longer has capital punishment in state cases, Christensen could have been sentenced to death because he was convicted in federal court. As the jury, which deliberated for over eight hours, did not reach a unanimous vote on the death penalty, Christensen was automatically sentenced to life in prison without the possibility of parole on Thursday.

He reportedly flashed a smile to his defense attorneys after the verdict was read.

Christensen abducted Zhang in June 2017 from a bus stop in Urbana, about 140 miles southwest of Chicago, by posing as an undercover officer, prosecutors said. Once back at his apartment, authorities say he raped, choked, and stabbed Zhang, then beat her with a baseball bat and decapitated her.

Zhang’s body was never found.

Christensen was implicated in the death when his then-girlfriend, Terra Bullis, wore an FBI wire to the vigil for Zhang’s disappearance; Bullis recorded Christensen telling her about how he raped and killed Zhang, whom he called his 13th victim. (An FBI agent during the trial said authorities have not yet been able to corroborate that Christensen killed another 12 victims but also haven’t ruled it out.)

When Christensen saw the crowd at the vigil, Bullis testified that he told her: “They’re all here for me.”

On the recording, Christensen called Zhang “valiant” in her fight to survive and said she was “stronger than any victim I’ve ever had.”

“I won’t tell you where she is. I won’t tell anyone. They will never find her,” he said.

In an effort to convince the jury to let him live, Christensen’s defense team had showed videos of him as a child.

But Assistant U.S. Attorney James Nelson said on Wednesday during the government’s closing arguments that “justice must be done.”

“Sentence Brendt Christensen to death,” he said. “All murderers start out as innocent children. Sometimes children grow up to be cruel adults. The defendant is not in here because of what he did when he was 12.”

“The defendant killed Yingying Zhang for sport,” Nelson added, explaining that Zhang’s family had so much hope for her bright future.

“That’s why Yingying fought so hard,” he said. “She had so much to live for.”

During the trial, prosecutors said that Christensen decided even before Zhang’s arrival in the United States that he would kill “a petite woman who could easily be disposed of” and that she was his “ideal victim.” Authorities told the jurors that Christensen approached a different young woman earlier that same day, posing as an officer, but that woman refused to get in the car.

Last week, Zhang’s family—and Christensen himself—cried as her father described the last time he saw her alive at a train station on her way to the U.S.

“She is part of me as if my life without her would not be complete,” Ronggao Zhang testified at Christensen’s sentencing. “To tell you the truth, I do not know how to live the rest of my life.”

“This wonderful daughter of mine, she is my everything,” Zhang’s mother, Lifeng Ye, said in her testimony. “Our entire family does not know how to carry on.”

Zhang’s fiancé, Xiaolin Hou, told the jurors that her death “totally changed the track of my life” and “took away the most important person in my 30 years of life.”

After Christensen was convicted, Zhang’s father said in a statement that her family “will not give up” on their wish to “find Yingying and bring her home.”

Christensen’s mother, Ellen Williams, testified during his sentencing that it would be “devastating” if her son was executed, and defense attorneys pointed to her testimony, as well as Christensen’s good behavior in jail, in their case for a life sentence.

In her closing arguments, federal defender Elisabeth Pollock asked for mercy for Christensen, emphasizing that he sought help for his mental health issues before ultimately killing Zhang.

“He’s leaving prison in a casket,” Pollock said. “The only question is when.”