PEORIA, Ill. (WAND)- Investigators confronted Brendt Christensen with video evidence and pressed him for information in a recorded interview played for jurors in Christensen's trial Thursday.

An FBI agent and a University of Illinois Police officer conducted the interview after midnight on June 15, 2017, as other investigators executed a search warrant on Christensen's black Saturn Astra. The car matched the one shown picking up Yingying Zhang in security video on June 9.

"Why am I under suspicion?" Christensen asked. "Is it just my car or is it anything else?"

The interviewers referred Christensen to an earlier conversation, in which he said he had been home at the time Yingying Zhang was shown getting into the car.

"I was either playing video games ... or taking an afternoon nap ... so I was unable to produce an alibi," Christensen said.

The investigators told Christensen they knew Yingying had been in the car.

"Believe me ... the full weight and force of the FBI is going to descend on that vehicle," Special Agent Anthony Manganaro. "I've got her getting into your car. I need to know why."

The investigators told Christensen video evidence showed the scholar enter his car.

"I've seen the videos, but I don't see me," Christensen said.

The investigators told Christensen they may have more videos, but would not show them to him. Then they suggested that he may have offered someone a ride.

Christensen then said he may have mixed up his days. He went on to admit picking up an Asian woman in her 20s on what he believed was Saturday.

"I did pick a girl up, I don't remember where," Christensen said. "I don't think it was her."

Christensen said he gave the woman a ride for a few blocks but said she "freaked out" when he made a wrong turn. He said he let the girl out of his car and last saw her standing and looking at her phone, but he could not say clearly where he let the girl out.

Christensen said the girl was in his car only about five minutes.

The investigators then asked Christensen about his marriage, suggested he may have been upset that his wife was away with another man, and asked him about sexual fetishes. Christensen said that his relationship with his wife was "vanilla."

After the interviewers further pressed Christensen, he said quietly "she rode in my car." He said he let the woman out and drove away.

Soon, he ended the interview.

"I think it's time that I stop answering questions," Christensen said. "I think I've tried to help enough."

After lunch, Christensen's defense argued that the jury should not have heard him ask to end the interview under court rules. They called for a mistrial, which the judge denied.

Next the FBI agent's testimony continued as he described how investigators sifted through hundreds of hours of surveillance video from around Champaign-Urbana. Prosecutors then played two sets of surveillance videos. The first set showed a black Saturn Astra moving from the area of the I-Hotel through campus on the morning of June 9. The second showed the car moving through campus around 2 p.m., picking up Yingying Zhang.

Investigators also obtained Amazon, UPS, and Busey Bank records for Christensen. They found that, on March 3, 2017, he ordered a Ledmark Heavyweight Cotton Canvass Outback Duffel Bag that measures 72" long, 22" wide and 22" deep. Records showed that Christensen returned the bag for a refund. Records also show that, on June 2, 2017, he ordered and received another of the same duffel bag. Investigators said they were not able to find the duffel bag, but they ordered another one, which prosecutors showed the jury.

Investigators also reviewed web search records for two Gmail accounts linked with Christensen, one named "Brendt Christensen" and one named "lovemachine689." The records showed searches on June 8 for developing cleaning products. A search on June 12 looked for how phone iPhone trackers work, even though investigators say Christensen didn't have an iPhone. In subsequent days, the records included news accounts of the search for Yingying and updates on the search from University of Illinois Police.

After a break, Christensen's defense cross-examined the agent. He admitted that many of the emails and search histories they recovered from Christensen's accounts were mundane and that the lovemachine698 account seemed to be primarily used for dating websites.

The defense pointed out that Christensen returned the first duffel bag around the time he sought counseling at the University of Illinois. They also pointed out that a witness told police she saw the bag in Christensen's apartment on the Monday after Yingying Zhang's disappearance and said he moved the bag easily.

They also referred to Christensen's claim, mentioned in opening statements, that he had killed 13 people including Yingying Zhang. The agent acknowledged that background checks, a DNA database search and more turned up no sign that claim is true.

Earlier in the day, investigators told jurors of long days spent searching for Yingying Zhang in 2017.

"Average was 20 hour workdays canvassing neighborhoods, canvassing vehicles ... anything we could do to determine where Yingying was," said FBI Special Agent Joel Smith.

Smith described digging through several "Big Belly" garbage bins at Centennial Park after cell phone data suggested Christensen may have been there. He also described searching an area near I-57 and County Road 1900 and searching a property known as Murdoch Mine in Douglas County. Those searches turned up nothing, he said.

Smith said he helped with a search of Christensen's car and apartment. He also testified that he interviewed "multiple sexual partners" of Christensen's but encountered no "red flags."

Prosecutors also called an asset protection worker for Schnucks to the stand. They played security cameras video that appear to show Christensen buying a bottle of spiced rum on the morning of June 9, the day Zhang was last seen.

They also showed video of Christensen buying groceries, drain cleaner and trash bags on the afternoon of June 12.