Seth Michael Roberts, 36, was found guilty of aggravated robbery on Wednesday by a Lubbock County jury.
Roberts was accused of using a handgun on September 2, to rob the Subway at 4923 34th Street. At the time, Lubbock ISD said nearby Coronado High School was put on lock down for about 20 minutes after the robbery.
Roberts was arrested for unrelated charges before police could identify him as the robber and press charges.
A jury deliberated for less than a half hour before finding Roberts guilty. The sentencing phase of his trial started Wednesday and might be complete on Thursday.