PEORIA, Ill. (WAND)- Brendt Christensen wept in court Wednesday as his father apologized to Yingying Zhang's family.

The defense called Christensen's father as their first witness in the sentencing phase of trial.

"I'm just sorry my son ... was the cause of their pain," Michael Christensen said through tears. Zhang's father and fiance had left the courtroom earlier in Michael Christensen's testimony.

The elder Christensen also described the pain of considering his son being executed.

"A couple days ago, I had a flash of him on the table, about to get injected ... I had to put it away," Michael Christensen said.

Michael Christensen said his son was a bright child who loved animals and took part in accelerated programs in elementary school.

"People would say I'm blessed," Michael Christensen said. "Brendt was easygoing, probably the most gentle person I ever met."

Asked by the defense, Michael Christensen said Brendt Christensen's paternal grandfather and uncle were both heavy drinkers. After her third child was born, Brendt Christensen's mother became depressed and drank heavily.

"She started drinking ... sometimes a quart of vodka or gin a day," Michael Christensen said. "She would drive (the children) drunk."

Brendt Christensen's defense has said he abused alcohol.

Michael Christensen said his son also suffered night terrors, beginning as a young child.

"We'd hear screaming from the bedroom," he said. "He was sitting straight up in bed. His eyes were open, but he didn't see me."

Doctors told the family Brendt Christensen would grow out of the night terrors, but he did not, Michael Christensen said.

Around age 15, Christensen jumped from a family deck onto a table, then ran into traffic and hit a moving van, Michael Christensen said. Christensen later told his father he knew he had been trying to kill himself but did not know why.

In an email to his father as an adult, Brendt Christensen said he continued to suffer two types of night terrors.

"The first are actual nightmares that always end up with me waking myself up by yelling really loudly," Brendt Christensen wrote. "They always have me approaching something very ominous."

The second type are sleep paralysis, Christensen wrote.

During cross-examination, prosecutors pointed to jailhouse phone recordings made shortly after Brendt Christensen's arrest in which Michael Christensen expressed anger at the Zhang family and said he believed his son would be exonerated.

"Brendt was arrested and people assumed right away ... the media, people commenting, that he was guilty," Michael Christensen told prosecutors.

Prosecutors also pointed out that, at the time of Brendt Christensen's arrest, Michael Christensen had not seen his son in person since 2013. The defense argued that was because Michael Christensen lived in a remote home Michigan, eight hours from his son's new home in Champaign-Urbana.

Christensen's attorneys have pointed to a family history of alcoholism, substance abuse and mental illness as mitigating factors in his sentencing.

Later in the morning, uncle Mark Christensen testified that he drank heavily for several years, at one point being charged with assaulting a police officer.

"I was laying on the floor of a jail cell, looking at the ceiling, wondering where I was," Mark Christensen remembered.

Mark Christensen said that Brendt Christensen's cousin and great aunt were also alcoholics, and he said one of Brendt Christensen's great aunts was institutionalized with schizophrenia.

Wednesday afternoon, Brendt Christensen's uncle Robert Lahmann testified that Christensen's maternal grandfather was a depressed artist who abused alcohol and who died after he stopped eating.

Lahmann also said Christensen's great-grandfather killed himself in 1973.

Lahmann said sentencing Christensen to death would dramatically affect his mother.

"It would just destroy her," he said. "She's not a strong person."

A teacher who led a gifted program that included Christensen also testified, remembering Christensen as a bright student who loved math, asked questions and loved playing outside.

"The young man I knew was brought up well, had his head on straight ... had passion, had the world open for him," she said. "I just couldn't understand what had happened."

Close family friend Deborah Mitchell, 59, also testified that Christensen's mother suffered depression after her third child was born and abused alcohol for many years.

"I would see her euphoric at times, and I would see her crashed out on the couch ... any time of day," Mitchell said.

Mitchell said she last saw Brendt Christensen in 2009, but continued to contact him through Facebook until 2016.

Michael Christensen, who has attended all of his son's trial, said he has been staying at a campground because he cannot afford to stay several weeks in a hotel.

"As a parent, I have to be here," he said during testimony. "I love him. Nothing's going to stop that."