The indictment of T.J. Lane came less than two weeks after a judge ruled he can be tried as an adult in the Feb. 27 shootings at Chardon High School in Chardon, Ohio, The (Cleveland) Plain Dealer reported.
Lane also faces two counts of attempted aggravated murder and one count of felonious assault in the shootings of three other students at the school.
Lane, who is being held in a juvenile detention center, could face life in prison without parole if convicted.
His defense attorneys, Ian Friedman and Mark DeVan, had argued Lane should be tried in Juvenile Court, where he could receive extensive therapy. The defense lawyers said Lane had serious mental health problems.
A professor of psychiatry at Case Western Reserve University testified Lane had an unspecified psychosis that included symptoms of schizophrenia, had lost touch with reality at times, and had a history of auditory hallucinations and involuntary fantasies.
Geauga County Juvenile Court Judge Timothy Grendell ordered Lane to be charged as an adult.
The Plain Dealer said the case is expected to hinge on whether Lane was sane at the time of the shootings.
Lane admitted firing 10 shots from a .22-caliber handgun, a police report showed.
Demetrius Hewlin, 16, Russell King Jr., 17, and Daniel Parmertor, 16, were killed.
Lane attended Lake Academy, an alternative school in Willoughby, and the bus that transported him there leaves from Chardon High School each morning.