KNOXVILLE, Tenn. (WVLT) -- Prosecutors have dropped all charges against a Halls High School teacher accused of having sex with a student.

The case against Corey DeHart just evaporated, according to John Gill, who serves as the special counsel to the Knox County District Attorney General.

Gill says several things changed since the alleged incident in September 2007, including the discovery of witnesses who contradict what prosecutors previously believed the evidence would show.

DeHart was placed on leave when he was charged.

The school system has not yet told us about DeHart's job status now that charges have been dropped.