Michael Christensen, father of Brendt Christensen, leaves the courthouse in Peoria, Illinois, U.S., July 8, 2019. (Photo: AFP)

Michael Christensen, father of convicted killer Brendt Christensen, testified in an Illinois court on Wednesday to save his son's life, telling the judges and jury about his son's childhood "night terrors," his love for animals, and his mother's alcoholism.

Christensen reportedly broke down as his father described how a death sentence would affect him.

The father testified for the defense before a jury that will decide whether his son should be executed for the 2017 kidnapping and murder of Chinese scholar Zhang Yingying or receive a life sentence in prison. Christensen was convicted by the same jury on June 24.

Wang Zhidong, lawyer of Zhang Yingying's family, said criminal sentence is usually determined by judges in most criminal cases except death penalty cases, which requires verdict from a jury, and death penalty is only possible when all 12 jurors agree on it, otherwise, Christensen will spend the rest of his life behind bars, without parole, rather than being handed a death penalty.

Ye Lifeng (2nd R), mother of Zhang Yingying, wails in grief after a federal jury finds Brendt Christensen guilty of kidnapping and murdering her daughter, outside the U.S. Courthouse in Peoria, Illinois, June 24, 2019. /VCG Photo

"I'm his parent. I have to be here. I love him. Nothing's going to stop that. I have no choice," said Christensen's father.

He told the court he could stand a death sentence, but not the actual death, adding he recently pictured Christensen about to be executed, but "I had to stop. I can't think of that too much."

Two of Christensen's friends also took the stand. One of them is Christensen's childhood friend Tom Mitchell who was born the same day as Christensen, in the same hospital. He said Christensen's mom was clearly an alcoholic and his mom told him not to let Christensen's mom drive him places if she appeared drunk.

Another is Christensen's best friend from high school, Andrew Kieper, who put 50 U.S. dollars on Christensen's jail telephone account so he could make calls a few days after he was arrested. He testified Christensen is a "goofy, fun-loving teenager. Nothing outside the usual."

Christensen's uncle also testified, describing him a "happy go-lucky kid ... just a real nice kid."

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A day before, Zhang's father, brother and fiance testified in the court, and a video testimony of her grief-stricken mother was also played out.

"I wanted to see her in a wedding dress," said Zhang's mother Ye Lifeng, adding that she was looking forward to her daughter's wedding in October 2017. "My daughter did not get to wear a wedding dress. I really wanted to be a grandma." 

"She is part of my life. My life without her will not be complete," said Zhang's father, Zhang Ronggao, adding that he and his wife have hardly been able to sleep over the past two years following the disappearing of their daughter, and they have been facing health issues. 

Prosecutors are trying to convince the jury to sentence Christensen to death, rather than a life sentence without parole, while the defense argues that life in prison, without parole, is punishment enough for Christensen.

China's Consulate General in Chicago, Hong lei, expressed sincere sympathy and deep condolences to Zhang's family during a visit to the University of Illinois Urbana Champaign last week. 

Hong said they would further urge the U.S. Department of Justice to pay close attention to this case, and conduct the trial justly in accordance with the law. Meanwhile, they would also cooperate with the university, and local organizations of overseas Chinese to provide help to Zhang's family.

The jury will soon decide Christensen's fate after hearing arguments from both sides during the sentencing phase of the trial.