More evidence and details emerged as prosecutors laid out their case in the federal death penalty trial of Brendt Christensen in the slaying of 26-year-old missing Chinese scholar Zhang Yingying, at the federal courthouse on Thursday.

Christensen, 29, a former physics graduate student at the University of Illinois, is accused of picking up Zhang at a campus bus stop, then raping and torturing her in his apartment, resulting in Zhang's death. The location of Zhang's body is still unknown.

Christensen's defense lawyer acknowledged in his opening statement on Wednesday that his client killed Zhang but disputed the prosecution's version of events.

FBI Agent Anthony Manganaro testified during the second day of the trial that Christensen's story kept changing when he interviewed him three days after Zhang's disappearance.

In a video of the FBI agent and campus police officer Eric Stiverson's interrogation of Christensen, the defendant initially said that he was playing video games all day at home during the time Zhang was captured on surveillance video getting into a black Saturn Astra, which was between 2 pm and 3 pm on the afternoon of Friday, June 9, 2017.

"Maybe I'm getting my days mixed up," said Christensen, after Stiverson described in detail they knew he was the one who picked her up.

He also insisted he had a hard time "telling Asian people apart" when asked why he didn't tell FBI agents about picking up an Asian woman.

Zhang looked "distressed" when he spotted her, said Christensen, adding that she spoke "broken English", said she was late to some place and had a meeting with her professor. He said he then offered her a ride.

Stiverson, however, pointed out later in the session that she Googled the address of One North — the apartment that she planned to sign a lease on that afternoon — one minute after she got into Christensen's car.

Christensen repeatedly claimed that he let Zhang get out of his car after she "freaked out" when he made a wrong turn, saying, "I don't want to keep someone I barely know in my car."

He admitted during the questioning that he was attracted to Zhang "a reasonable amount".

Both Manganaro and Stiverson pointed out that based on what they knew, she "didn't get out" of his car.

"At this point we are trying to help you. We are trying to help her. We are trying to help her family," said Stiverson, trying to convince Christensen to tell the truth.

"Where'd you take her, Brendt? We need to find Yingying," said Manganaro, who told him earlier that Zhang's parents had traveled from China to look for her. A group of 600 Chinese students also joined the search.

Christensen answered, "I think it's time that I stop answering questions" and referred to the presence of a lawyer.

The FBI agent said he was later detained for lying to federal agents, but was released not long after.

Manganaro presented other video evidence showing Christensen driving around the UI campus both in the morning and early afternoon on the day Zhang went missing.

He also showed his two-time purchase record of a 72-by-12-inch duffel bag — one in early March that was later returned, and one on June 3. A bag of the same model — almost the same size as an adult — was purchased by Manganaro during the investigation and was presented to the jury.

The defense noted that the bag was still in Christensen's apartment as of June 12, 2017, according to his wife, who saw him carrying the bag out without much difficulty.

Also revealed by Manganaro was Christensen's Google search history, which showed that he had searched for "how iPhone tracker works", "obstruction of justice" and, multiple times, for updates on the search for Zhang between June 9, when Zhang disappeared, and June 30, when he was arrested.

Besides the FBI agent's testimony, the jury also saw surveillance video from a Champaign grocery store showing Christensen buying a large bottle of rum at 7:45 am on the morning of Zhang's disappearance.

The court proceedings will resume at 9 am on Friday.