Yet most of the time Shi and Sun were with the Zhang family, they were not filming. "Let me put it this way: many times we visited them, we did so not for the purpose of filming," Sun says. "We would bring our camera and put it in a corner of the room. Other times the parents told us that they didn't want to be filmed and they still wanted to have us for dinner. We always obliged."

Asked what trait he thought Zhang had in common with her parents, Sun said,"Trusting".

He's probably right. In one of her diary entries, Zhang wrote, "I told mom that there are both Americans and Chinese here－all extremely nice."

In retrospect, some footage was eerie. In one of the earliest scenes Shi captured, in the summer of 2017, Zhang's maternal aunt, on a random search on the street, pointed to a few dumpsters not far away and said, "I really want to fumble around in that... but I'm afraid we aren't allowed to..."

During Christensen's trial between June and July last year, the Zhang family were told that "after killing Yingying Zhang, Christensen placed her bodily remains into garbage bags in the dumpster immediately outside his apartment building", to quote Steve Beckett, the family's other lawyer.

"The contents of the dumpster were taken to a private landfill. It was determined that by the time Christensen's attorneys disclosed his statement to the federal authorities (in late 2018), the content of the dumpsters that contains Yingying's remains would have been covered by at least 30 feet of fill," Beckett told media after the trial.

Yet for the family who had waited for nearly two years before flying in to attend the trial, emotional devastation was done right on the case's opening day, when the gruesome details of Zhang's death came to light.

"Although the FBI must have obtained those details through Terra's audio surveillance back in 2017, it was only toward the end of 2018 when our lawyers emailed me about what they had just been told by federal prosecutors about Yingying's death," Hou said.

Unable to find a way to break the news to Zhang's parents, Hou alerted the volunteer translators before the court opening."I told them to bypass the details," he said."But it didn't take long before Yingying's father knew－it was everywhere in the American and Chinese media."

"He became more silent from that day on," said Shi, who sat in the courtroom every day with Sun throughout the trial. Previously, the two had rented a house in Peoria, a town 90 minutes' drive from Champaign where the trial took place.

"For long hours he sat on the stoop of the family's temporary residence in Peoria, smoking nonstop. Occasionally he would let out a sigh, as if to release some of the anger and anguish that had been brooding inside his chest," Shi says.

During Bullis' court appearance, Shi gave a written note to a court worker who agreed to pass it on to her."I told her who I was and what I was doing," Shi said."She contacted me, and we became the very first to film her interview."

According to Bullis, despite speculation that the FBI may have forced or manipulated her, or have paid her, it was she who had asked, from the very beginning, "Is there a way I can help?"

Upon her own request, Bullis sat down with the Zhang family at the end of the trial. Having practiced with Shi, Bullis, who learned Chinese in high school, read a letter to Zhang's parents in Chinese.

"I drew on your love for Yingying to fight off the terror I constantly felt doing what I was doing for the FBI," said Bullis, who burst into tears with relief when Yingying's mother told her that "you are brave and just as kind as my daughter".

On June 24, 2019, the jury convicted Christensen of kidnapping resulting in the death of Zhang Yingying, a crime considered in legal realms as severe as murder.

On his drive back from Peoria to Chica-go, Wang, who had spent a thousand hours on the case, parked his car by the roadside and wept.