A Colorado man accused of threatening to kill President Barack Obama and blow up a suburban Minneapolis mall has pleaded not guilty. Twenty-year-old Timothy Gutierrez of Cortez appeared in federal court in Durango on Tuesday for arraignment and a detention hearing. He was ordered detained without bond. Gutierrez is charged with sending threatening e-mails to the FBI in Washington, D.C. Prosecutors say the first e-mail threatened Obama, and the second said explosives would be used to damage or destroy property at the Mall of America. Gutierrez has said the threats were a prank. He turned himself in January 29 at the FBI's office in Durango.