Matthew Milby, now in his 20s, is accused of opening fire during a May 2018 graduation rehearsal at the high school, located about 100 miles west of Chicago. School Resource Officer Mark Dallas shot and wounded Milby; no one else was injured.
Lee County State's Attorney Amira D. Fox confirmed Wednesday that Milby was found fit to stand trial Tuesday. He was deemed unfit previously in both 2018 and 2019.
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He faces several charges, including aggravated discharge of a firearm and attempted murder.
His attorney said he's considering filing a motion for a change of venue.
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Milby has also been charged with unrelated battery charges, stemming from an alleged fight that took place during his detainment.
Milby's mother said her son was bullied in school, and he was a good kid. Illinois State Police later said Milby used his mother's gun in the alleged shooting.
The video in the player above is from an earlier report.