26-year-old Yingying Zhang was last seen on at the University of IL on Friday 9 June.
When the investigators interviewed Christensen a second time, and pointed out the two cars looked identical, the suspect admitted he had driven around the University of IL campus on June 9 and had given a ride to an Asian female who told him "she was late for an appointment".
Security video showed Zhang entering a black Saturn Astra in Urbana about 2 p.m. on June 9.
Christensen studied physics in the graduate program at the university and previously was a research assistant at the University of Wisconsin-Madison, according to his LinkedIn page.
In April, Christensen visited online forums and viewed threads with titles such as "Abduction 101" and "planning a kidnapping". The FBI said in a statement that evidence they have points to Zhang no longer being alive.
Zhang had a year-long position at the university's department of natural resources and environmental sciences.
Federal Bureau of Investigation revealed Brendt Christensen, 27, has been arrested in connection with Zhang's disappearance.
Authorities believe Christensen spotted Zhang at a bus stop, then circled around the block back to her location to speak with her. Zhang had been on her way to speak to the manager of a building where she was going to be leasing a new apartment.
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In a recording of the conversation, according to the affidavit, Christensen was heard talking about keeping Zhang against her will to his apartment.
The footage below is the last time Yingying Zhang was seen in public.
The vehicle pulled over to where Zhang was standing, and she was observed on surveillance video speaking with the driver for about a minute.
There are more than 300,000 Chinese students in the U.S.in all.
They placed him under surveillance and say he searched the internet on how to kidnap people. He will make his first appearance in federal court on Monday.
Friends and family said Zhang dreamed of one day landing a professorship and being able to help her parents financially.
Authorities declined comment when asked if they had any leads on where Zhang's body might be located.
There are more than 300,000 Chinese students attending schools in the US, and Zhang's disappearance and now suspected death, has triggered widespread concern in China. Lance Cooper, of the University of IL.
"We hope they are wrong, but trust they have creditable information to make this statement", organizers Kim Tee and Randy Tom said in a joint email late Friday night.