Courtesy of Christine Cornell(CHICAGO) -- The killer of a young Chinese visiting scholar who was studying at the University of Illinois Urbana-Champaign (U of I) can be heard chuckling in an audio recording obtained by ABC News after he says that he "hit her with a baseball bat" and decapitated her.

Brendt Christensen, a now-30-year-old former teaching assistant at the university, described to an FBI informant on secretly recorded audiotape how he kidnapped and killed Yingying Zhang shortly after picking her up on June 9, 2017.

Zhang, a 26-year-old Chinese visiting scholar and agriculture researcher at U of I, was last seen on video entering a black Saturn Astra on June 9, 2017. Although Christensen had pleaded not guilty, his own attorney admitted Christensen kidnapped and killed Zhang in his opening statement earlier this month. The defense added that it took issues with "the way the government says the events occurred."

Terra Bullis, Christensen’s girlfriend at the time, agreed to secretly record him for the FBI. Bullis recorded Christensen a total of nine times in June 2017. Christensen’s alleged confession took place while the two were attending a campus vigil for Zhang.

"Did she fight?" asked Bullis, who wore an undercover wire, in the recording.

"More than anyone else," replied Christensen.

In the recording, Christensen says Zhang was his 13th victim. "She was stronger than any victim I have ever had."

The audio recording took place on June 29, 2017, the day before Christensen was arrested.

In the recording, Christensen says Zhang was his 13th victim. "She was stronger than any victim I have ever had."

The audio recording took place on June 29, 2017, the day before Christensen was arrested

Christensen's lawyers argued that he was intoxicated when this conversation was recorded and that he exaggerated his claims. Bullis, who testified in court last week, told defense attorney Robert Tucker that although Christensen was drinking, he was not drunk.

On the recording, Christensen went on to describe to Bullis what he did to Zhang in detail. "I just cut her clothes off and just started doin' stuff to her," Christensen is heard saying.

Also in the recording, Christensen is heard describing Zhang's "valiant" efforts to fight back, saying it was "supernatural, almost, how [Zhang] just didn't give up."

Bullis told jurors that at the time Christensen seemed "boastful.”

After claiming he sexually assaulted her in his bedroom, Christensen is heard on the tape saying he was surprised she was "still alive." He tells Bullis that he eventually took her to the bathroom, attacked her with a baseball bat, and decapitated her.

"So I chopped her head off and said that was the end of it," Christensen said with laughter, which could be heard on the recording.

Bullis testified that Christensen said he "admired" serial killers like Ted Bundy.

"The last person I would ever consider at my level that actually did anything was Ted Bundy," Christensen is heard telling Bullis in the recording while commenting on the "legacy" he wishes to leave behind.

"Do you really think that you might be the next successful serial killer?" asked Bullis.

"I already am," replied Christensen. "I already am."

Prosecutors and investigators alike say they have not found any evidence linking Christensen to other crimes. In the audio, Christensen says Zhang’s case is the first to put him on investigators’ radar.

"Yingying is the only person that has produced evidence that leads back to me," Christensen is heard telling Bullis. "Number 13.”

When Bullis inquires about the whereabouts of Zhang's body in the recording, Christensen says he'll never tell.

He goes on to say Zhang's family will "leave empty handed."

Zhang’s father was present in court last week when this audio was played for the first time. He received a Chinese translation via a one-way headset. He kept his head down throughout the recording, but stared directly at Christensen upon its conclusion and held his gaze until the end of the day’s court proceedings.

Christensen was found guilty Monday on all counts: one count of kidnapping resulting in death and two counts of providing false statements to the FBI. It took the jury less than 90 minutes to reach a verdict. Christensen is expected to be sentenced in mid-July and could face the death penalty.

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