(CNN) -- A 17-year-old accused in a high school shooting that left three dead in Ohio pleaded not guilty Friday, and his bail was set at $1 million.
T.J. Lane was indicted in the shooting deaths of three classmates at Chardon High School. A judge ruled last month that he could be tried as an adult.
Lane sat quietly during Friday's brief proceedings, answering a few questions from Geauga County Judge Forrest Burt.
Lane's attorneys said they reserved the right to enter a later plea of not guilty by reason of insanity.
Authorities allege that on February 27, Lane walked up to a table at the high school cafeteria and started firing.
"He was silent the entire time," said Nate Mueller, who was a few feet away from the gunman. "There was no warning or anything. He just opened fire."
A teacher identified as Frank Hall helped chase the gunman out of the school. Police arrested Lane a short time later.
When the violence ended, six students had been shot, and in the following days, three died: Daniel Parmertor, 16; Demetrius Hewlin, 16; and Russell King Jr., 17.
Days after the attack, prosecutor David Joyce said Lane admitted taking a .22-caliber gun and a knife into school that morning and firing 10 rounds, choosing his victims randomly.
Joyce said that in the months since the bloodshed, he has met with the families of the victims on a constant basis.
"Their child was murdered," he said. "Justice for them would be to see Mr. Lane detained for an extended period of time."
Though Lane could be tried as an adult, federal law prohibits capital punishment for anyone under the age of 18.
"Obviously, he can't be put to death as a juvenile, but he can certainly be sentenced to life without parole," Joyce said. "That's up to a jury to decide."
Lane was indicted on six charges: three counts of aggravated murder, two counts of attempted aggravated murder and felonious assault.
Burt ordered Lane to a juvenile detention center until June 18, when he will be transferred to the Geauga County Jail.