On the evening of June 29, 2017, as dozens of University of Illinois students walked the streets and raised a banner that said, “Help find Yingying Zhang,” Brendt Christensen stood on the sidelines and told his girlfriend why Zhang would never be found.

Zhang, a visiting scholar from China, had disappeared less than two months after arriving in the United States. One afternoon, she had taken a break from her studies on photosynthesis in corn and soybeans to grab lunch and sign a lease for a new apartment. But Zhang never made it to meet the property manager. She was last seen on city surveillance cameras flagging down a bus, then getting inside a black Saturn hatchback that pulled up alongside her. Before long, her family flew from China to start looking for her.

“We searched the parks, the abandoned houses,” her boyfriend, Xiaolin Hou, told a federal court this month. “We don’t have a destination but we will never give up the hope to find her.”

Only Christensen knew where she was. As he would soon tell his girlfriend, standing in the crowd at Zhang’s memorial, Christensen kidnapped her. He raped her and killed her and disposed of her body where nobody would ever find it, he said.

The 29-year-old student instructor and doctoral candidate had been spinning the dark plot around in his head for months, leading a “double life,” prosecutors said, as he staked out random victims on the streets of Champaign, Ill., until he found Zhang. He wanted to fulfill an “abduction fantasy,” prosecutors said. He idolized Ted Bundy, telling his girlfriend that afternoon that Zhang was his 13th victim (a claim his defense attorney claimed was drunken nonsense) and that he was “apparently very good at this."

“The family won’t leave until she is found,” Christensen said. “They are going to leave empty-handed, because they will never find her.”

His girlfriend, Terra Bullis, prodded him along to keep talking: She was wearing a wire.

On Monday, a federal jury convicted Christensen of kidnapping resulting in death after prosecutors presented his graphic recorded confession, twisted Internet history and the evidence found in his home, including blood in his room that belonged to Zhang. Christensen may now face a life sentence or the death penalty, a punishment that federal prosecutors and Zhang’s family are seeking but that Christensen has avidly sought to halt. His defense attorneys admit Christensen killed Zhang, but say he is a mentally ill man who should not be executed.

“It will be startling for many of you to hear: Brendt Christensen is responsible for the death of Yingying,” defense attorney George F. Taseff admitted to jurors in a jarring opening statement, according to a transcript of the trial. “So in view of what I just said, some of you may be asking, why are we having a trial in this first stage? The answer to that is that Brendt Christensen is on trial for his life."

Zhang, 26, moved to Illinois from China in April 2017 to pursue a doctoral degree in crop sciences, hoping to later return to China to teach at a university. She and her longtime boyfriend planned to marry in October 2017. But as she stuck to her studies, somewhere else on campus, Christensen delved into a dark world.

“She didn’t know that before she even came to this country,” federal prosecutor Eugene Miller said, “the defendant had gone down this dark path that led to this very moment.”

Christensen first opened up about his ideas on abducting and killing a random person while visiting university counselors in March 2017, Miller said in court. He said he was feeling suicidal because his wife wanted to leave him because he couldn’t get a handle on his drinking and drugs. He had just dropped out of his doctoral program to take a master’s track instead while maintaining his teaching position. But the counselor noticed he had also checked off the box about thoughts of harming others. Why? she asked.

He started talking about Bundy, the serial killer who “fascinated him,” Miller said.

“He admitted that he had gone pretty far down the path of thinking about abducting and killing someone, including how to do it, and admitted he’d identified the type of victim he would choose,” Miller said. But Christensen claimed that he didn’t have those thoughts anymore.

His Internet search history said otherwise.

In April 2017, he started frequenting a forum called “Abduction 101” on a website for BDSM fetishes; Bullis, whom he met on OkCupid with the permission of his wife, had introduced him to the world of BDSM, prosecutors say. On the forum, he joined chats about the “perfect abduction fantasy” and “planning a kidnapping.” He wrote online that he would buy a duffel bag big enough to fit a body inside, and soon, when his wife went out of town for the weekend in June, he bought one off the Internet.

And then he started prowling the streets.

First, he spotted a young woman walking by herself toward a bus stop and pulled up next to her, wearing a black T-shirt and mirrored aviator sunglasses. He said he was an undercover cop, and could he ask her a few questions? She said yes. He asked her to get in. She said no.

He kept driving, and then there was Zhang. She was running late that day, having missed the connecting bus route to the apartment where she planned to move to save money. Christensen offered her a ride. She got in.

Zhang’s seemingly random disappearance alarmed the Chinese student population at the University of Illinois. Her boyfriend, Hou, said “Yingying is such a soulful girl,” one who would “never let others worry about her,” and so he knew something terrible must have happened. Hou and Zhang’s family got on a plane to the United States to start looking for her. Even parents of other Chinese students flew to Champaign just to be with their children as anxiety gripped the campus, the Daily Illini reported in June 2017.

Christensen followed the news coverage with interest, as he learned investigators had already spotted his black Saturn Astra on surveillance. He eliminated every trace of the crime that he could think of: Drano for the blood that went down the bathtub sink, bleach for the blood on the carpet and the bedroom walls. And by the time police came knocking, Miller said, “[Christensen] was able to get rid of almost all of the evidence.”

But he forgot a few things, Miller said: “He didn’t clean behind the baseboard. And he didn’t clean under the carpet.”

There, police found blood. They found blood on the mattress, and they found a Louisville Slugger baseball bat. The blood was nearly invisible — but it was there, too. All of it was Zhang’s, forensic analysts would soon find.

Police enlisted Bullis to talk with him while wearing a wire for the FBI. Finally, he made her come to the memorial for Zhang, where he spilled all. He told her Zhang never stopped fighting.

The FBI is still investigating Christensen’s recorded claim that Zhang was his 13th victim, and that he had been killing women since he was 19, as an agent testified during the trial. No evidence has emerged in two years to corroborate Christensen’s claim, but that does not mean it’s “impossible,” the agent testified, as CBS Chicago reported.

Zhang’s body has still never been found.

But after the trial ended, the family gathered outside the courthouse Monday and said they were still looking. Zhang’s mother cried as Zhang’s father tried to read from a piece of paper, stopping to console his wife. Their attorney read the family’s brief statement in English.

“Our wish has always been to find Yingying and bring her home,” the statement said. “We’ll not give up.”

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