A 28-year-old graduate student who federal authorities said had recently visited an online "fantasy abduction site" has been charged with kidnapping a visiting Chinese scholar at the University of Illinois who disappeared three weeks ago and is now presumed dead.

Brendt Christensen was charged on Friday, his 28th birthday, with kidnapping Yingying Zhang, a visiting scholar in the Department of Natural Resources and Environmental Sciences at the University of Illinois Urbana-Champaign who went missing June 9.

The FBI said they tracked down Christensen through surveillance video showing the 26-year-old Zhang getting into his black Saturn Astra four-door hatchback around 2 p.m. after apparently missing her bus.

The federal complaint said authorities also captured an audio recording of Christensen in which he said he had brought Zhang back to his apartment and held her against her will.

USA vs. Brendt Christensen

Zhang had arrived at the university in late April and was on her way to sign a lease at an apartment when she went missing.

While authorities publicly declined to discuss Zhang's fate, the federal complaint said law enforcement "does not believe (she) is alive."

Zhang's father, who arrived from China last month after his daughter's disappearance, had joined a march by hundreds in Urbana in support of the missing scholar.

In a statement, UI Chancellor Robert Jones said the entire campus is "saddened" by the news of Zhang's apparent death.

"This is a senseless and devastating loss of a promising young woman and a member of our community," he said.

Zhang was among some 5,600 Chinese enrolled at the University of Illinois Urbana-Champaign, more than at any U.S. college, according to government data. There are more than 300,000 Chinese students in the U.S. attending universities.

"I ask all of you to help to ensure that Yingying is remembered for her kindness, her gentleness and her smile. This is the greatest gift we can offer as a community to her family and friends today,"Jones added.

Those who knew Zhang described her as bright and outgoing. She played guitar and sang in a band called “Cute Horse” in China. One of her favorite songs was “The Rose,” a hit in 1980 for American singer Bette Midler.

Zhang’s boyfriend has said that she was also cautious and wouldn’t normally get into a car with a stranger unless duped or forced.

Authorities said they initially questioned Christensen, a graduate teaching assistant in physics for four years, after pairing him with the type of car seen in the video, but that he said he could not recall his whereabouts on the day Zhang disappeared. Christensen is also a graduate of the University of Wisconsin-Madison, where he majored in physics, and he is from Stevens Point, Wisconsin, according to his Facebook page.

After re-examining the video, FBI agents noted that Christensen's car had a sunroof and cracked front passenger hubcap that matched the car in the video.

They also found in a later examination that the side of the car where the victim would have sat had been "cleaned to a more diligent extent than the other vehicle doors," indicating an effort to conceal or destroy evidence.

A subsequent search of the suspect's house produced Christensen's phone that showed that in April he visited a forum entitled "Abduction 101" that included sub-threads "perfect abduction fantasy" and "planning a kidnapping," the federal complaint said.

Authorities said Christensen, in a second interview, admitted to picking up Zhang, who had appeared distressed after missing her bus. But he said that while trying to navigate using her cellphone map, he told her that he thought he had a wrong turn and that Zhang "panicked."

Christensen then told authorities he let her out of the vehicle in a residential area a few blocks away.

Contributing: Associated Press