A man was charged Friday with kidnapping a visiting University of Illinois scholar from China who authorities believe to be dead after she disappeared three weeks ago. A federal criminal complaint alleges the suspect’s phone was used to visit an online forum in April called “Abduction 101.”

Yingying Zhang, the 26-year-old daughter of a working-class factory driver from China, disappeared on June 9, just weeks after arriving at the Urbana-Champaign campus in central Illinois where was doing research in agricultural sciences and was expected to begin work on her doctorate in the fall. Friends and family described her as extremely bright, hardworking, caring and devoted to her parents.

Some 5,600 Chinese students are enrolled at the university — more than at any other college in the nation — and Zhang’s disappearance fed anxieties of families of Chinese students studying in the U.S.

Federal authorities say Brendt Christensen, who turned 28 on Friday, of Champaign, Illinois, is charged in a criminal complaint with abducting Zhang shortly after she stepped off a bus near the university campus. Video shows her getting into the front seat of a black Saturn Astra.

According to the 10-page affidavit filed in federal court by FBI Special Agent Anthony Manganaro, Christensen was under surveillance Thursday when agents overheard him explaining he kidnapped Zhang. Authorities say based on that and other facts uncovered during the investigation, agents believe Zhang is no longer alive.

Asked Friday night if authorities had any leads on where Zhang’s body might be located, the spokesman for the FBI Springfield office, Bradley Ware, declined comment.

Christensen will remain in custody pending his initial federal court appearance, which is set for Monday in Urbana.

Illinois Chancellor Robert Jones said in a statement the campus community is saddened by the news Zhang is believed dead.

“This is a senseless and devastating loss of a promising young woman and a member of our community,” Jones said. “There is nothing we can do to ease the sadness or grief for her family and friends, but we can and we will come together to support them in any way we can in these difficult days ahead.”

The federal charging document says one of the threads on the forum that Christensen’s smartphone visited online in April — months before Zhang went missing — was entitled, “Perfect abduction fantasy.” Another was about “planning a kidnapping.”

According to Manganaro’s affidavit, investigators determined there were 18 vehicles similar to the one Zhang got in that were registered in Champaign County.

The vehicle belonging to Christensen was first observed in an apartment complex parking lot on June 12 — just days after Zhang went missing — and investigators questioned him. The affidavit stated that investigators noted Christensen couldn’t recall what he was doing on the day Zhang disappeared. They searched the vehicle but didn’t remove anything.

Investigators later determined the car in the video had a sunroof and cracked hubcap, like the vehicle belonging to Christensen, according to the affidavit. When investigators interviewed Christensen again, he admitted to driving around the University of Illinois campus and giving a ride to an Asian woman who said she was late for an appointment.

Christensen said the woman panicked after he apparently made a wrong turn and he let her out in a residential area.

The court document indicates a search of Christensen’s car indicates the area where Zhang was believed to have been sitting had been cleaned.

Christensen was placed under continuous surveillance on June 16, and on Thursday he was captured on an audio recording explaining how he took Zhang to his apartment and held her against her will. The affidavit says the woman remains missing.

Zhang’s father, Ronggao Zhang, traveled to Illinois from Nanping, China, to be closer to the search and take part in vigils. On Thursday, he took part in a walk with students and university staff to the corner where his daughter was last seen.

“We will forgive you. But please, let Yingying go,” he said last Sunday during an Associated Press interview, pleading to whoever abducted her.

Friends and family said Zhang dreamed of one day landing a professorship and being able to help her parents financially. She saved some of her income as a researcher to buy items for her mother and father including a microwave and a cellphone.

Zhang graduated last year with a master’s degree in environmental engineering from one of China’s elite schools, Peking University Shenzhen Graduate School. She had been doing research on crop photosynthesis, which included using drones to study fields.