Brendt Allen Christensen, 28, has been charged with the kidnapping of visiting Chinese scholar Yingying Zhang.

According to Sinovision, Christensen is a PhD candidate in experimental condensed matter physics at the University of Illinois at Urbana-Champaign and has served as the university's teaching assistant since 2013.

The criminal complaint against Christensen filed in federal court on Friday says that Christensen had read up on abducting someone online and the area where Zhang was believed to have been sitting inside his car had been cleaned.

Zhang has not been found. According to the US attorney's office, Zhang is believed to be no longer alive.