There is no closure for the families of Zhang and her killer Brendt Christensen. Two years of emotional torture, according to both families.
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For the first time, we hear from the killer's father.
"If for some dumb reason, the jury found him not guilty - juries do the weirdest things - I would've tried to have him committed because you can't have somebody that can do something like this out in society. You can't. But could he be treated? I think so," said Mike Christensen.
In an exclusive interview, Christensen tells ABC's Bob Woodruff something must have snapped that day in June 2017 when his son kidnapped and killed 26-year-old Yingying Zhang. Christensen was convicted this summer and is currently serving a life sentence with no chance for parole.
Originally, the elder Christensen said he thought his son was innocent.
"Well, I wasn't privy to a lot of the information that was out there initially," Christensen told 20/20. "I knew there was a good possibility. Many of the things that he did, I've done in my life. I've gone on websites and researched things that people would say, 'Why on earth would you do it?' To learn about it. That's what I do."
Christensen also said he believes his son was exaggerating during secretly-recorded conversations with his then-girlfriend Terra Bullis.
"Terra conducted seven in-person recordings with us, as well as two additional that were over the phone. So there was definitely, as those recordings went, an increase in the amount of information," FBI Special Agent Anthony Manganaro told 20/20.
"I believe he hit her with a baseball bat. Raped her? Doubt it. He even said he didn't. But also, choked her for 10 minutes? Now, one-handed, his bad arm, 10 minutes? And she's still alive? Does that make sense to you, sir? Somebody that strong and somebody that little choking for minutes? That doesn't make any sense to me either. That does not jive with the evidence. He was embellishing," Christensen said to Woodruff.
The I-Team has learned Christensen's legal defense team agrees and also believes the killer was lying when he said Yingying was his 13th victim.
Federal investigators have not ruled it out.
"So, unfortunately, there are many people who are missing in this country. So, the answer is we have no evidence that he has 12 other victims. But, given what he did in the case, it's certainly, certainly a possibility," said Assistant U.S. Attorney Eugene Miller.
Yingying's parents are still grieving the murder of their beloved daughter. Her body never found, the family still hoping to someday bring her home. Post-trial it was revealed Christensen told his attorneys he put Yingying's remains in three separate garbage bags and placed them in a dumpster outside his Champaign apartment. Based on that information, authorities say her remains could be scattered in nearby landfills.
After learning this information, Yingying's father said through a translator, "If Yingying's remains are ever found, we will return to take her home to China where she belongs."
Christensen's attorneys say they shared this information early on, hoping for a plea deal, but prosecutors say any deal was contingent on Yingying's remains being found.
"He did not believe that she would ever be recovered. And, as he said on the tape, 'She's gone. She's gone forever. She'll never be found'," said Miller.
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