CHICAGO (CBS) — Prosecutors are expected to wrap up their case against former University of Illinois student Brendt Christensen on Friday in the murder of Chinese scholar Yingying Zhang.

Christensen’s lawyers are expected to put on a brief defense, starting with testimony from his ex-wife, who was divorcing Christensen at the time Zhang disappeared in 2017, and was out of town with a boyfriend.

Brendt Christensen. (Courtesy: Macon County Sheriff’s Office)

On Thursday, Christensen’s former girlfriend, Terra Bullis, spent hours on the stand, testifying that Christensen borrowed her phone while the two attended a memorial walk for Zhang, typed the words “It was me. She was number 13. She is gone. Forever,” and then deleted them.

Bullis also said Christensen told her the crowd that night was there for him.

Christensen didn’t realize she was wearing a wire for the FBI, who had begun investigating him for Zhang’s disappearance.

Later that night, on the walk home, Christensen is heard on tape describing in graphic detail how he raped and killed Zhang.

Christensen was arrested the next day.

Defense attorneys have questioned how much the two had been drinking that night, and whether Bullis egged Christensen on at all to say the things he said.

The defense already has admitted Christensen killed Zhang, during their opening statement in the case, and appear to be setting the stage to ask the jury to spare him the death penalty.

Although Illinois repealed the death penalty in 2011, Christensen was charged in federal court, so can still face the death penalty in the case.

Christensen’s attorneys have tired to paint him as a man with mental health and substance abuse problems, who does not deserve to die for his crime.

The defense has said it should take about half a day for them to make their case.

Closing arguments likely would begin Monday before the case goes to the jury. If jurors convict Christensen, the next step would be the penalty phase of the trial, when a jury would decide if he should face the death penalty.