CHICAGO (CBS) — Cold, calculated and months in the making — that’s how federal prosecutors described the murder of Chinese scholar YingYing Zhang to a federal jury that will now decide if her killer should live or die.

Monday was the first day of Brendt Christensen’s sentencing hearing. Christensen’s death penalty hearing is expected to last several days.

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Unlike prosecutors, who want the death penalty, his defense attorneys will argue he deserves to live, in part because of his ongoing struggle with mental health issues.

Christensen’s interrogation with police is some of the evidence federal prosecutors may now use to convince the jury to give the former University of Illinois doctoral student the death penalty.

Last month the same jury convicted Christensen of picking the Chinese scholar up in his car then taking her to his apartment and choking, beating, stabbing and ultimately decapitating her.

Zhang’s body has never been found.

The case was tried in federal court, which still allows juries to hand down a death sentence despite the state’s ban on capital punishment.

In court Monday prosecutors told the jury the crime deserves “extraordinary punishment” and added that Christensen also deprived Zhang’s family of being able to give her a proper burial.

“There will be no closure,” he told the jury.

Zhang’s family, including her mother, who was inconsolable after Christensen’s conviction, is expected to take the stand with the help of a translator.

Defense attorneys will point to Christensen’s mental health struggles and the fact that he even sought help prior to Zhang’s murder. They are likely to argue he did not get the proper treatment.

The defense wants Christensen to get life in prison without parole and pointed to his good behavior in jail since his arrest.

Ultimately it will be up to the jury to decide his fate.

In addition to calling witnesses, videos made by some of Zhang’s friends were also played for the jury.

It’s possible Christensen himself could testify with one theory being he might choose to reveal what he did with Zhang’s body as a way to save his life.