Brendt Christensen, the accused kidnapper of Chinese scholar Zhang Yingying, pleaded not guilty to charges against him on Thursday during his arraignment at a federal court in Midwest U.S. state of Illinois.

The arraignment in a federal courthouse in Urbana of Illinois lasted not more than five minutes, and Christensen broke his silence, speaking some time during the proceeding.

In a statement, Christensen's attorney Anthony Bruno said: "he's demanded a jury trial and he plans to persist in his plea of not guilty."

Christensen's next pretrial hearing was set for 2:45 p.m. on August 28, and his trial date is set for Sept. 12.

Zhang, a visiting scholar at the University of Illinois at Urbana-Champaign (UIUC), was last seen entering a black Saturn Astra car driven by 28-year-old Brendt Christensen on June 9.

Police arrested Christensen for kidnapping 26-year-old Zhang on June 30, but Zhang's location is still unknown.

The FBI believes Zhang is deceased, based on facts presented in court and court documents and other facts uncovered during the ongoing investigation.

Christensen was indicted on July 12 by a federal grand jury on a criminal charge related to Zhang's abduction. He has been remaining in custody since then.