A martial arts instructor from southwestern Illinois has been sentenced to 90 years in prison for sexually abusing three young students.  The Belleville News-Democrat reports 20-year old Christopher M. Horton of Highland was sentenced Friday by U.S. District Judge David Herndon.  Horton pleaded guilty in October to five counts of sexual exploitation of a minor and one count of attempted sexual exploitation of a child.  Federal prosecutors say Horton recorded video of himself committing sex acts on students ages 6, 8 and 10.  Horton taught martial arts to the victims at a Belleville studio. Police questioned Horton after someone discovered one of the videos and contacted law enforcement.  Prosecutors say they recovered 57 video files from Horton’s cell phone.  He also was ordered to pay $3,250 restitution.