T.J. Lane, 17, admitted taking a .22-caliber pistol and a knife to Chardon High and firing 10 shots at a group of students sitting at a cafeteria table Monday morning, Prosecutor David Joyce said. He said Lane didn't know the victims.
Lane will probably be charged with three counts of aggravated murder and other offenses, the prosecutor said.
A thin figure with short dark hair, Lane seemed small next to the sheriff's deputies who led him into court, and said little more than "Yes, sir" in response to questions from the judge.
His face twitched lightly while the prosecutor recounted the attack, and he sniffled and half-closed his eyes as he left the courtroom under guard.
The hearing came hours after the death toll rose to three, and as schoolmates and townspeople grappled with the tragedy and wondered what could have set off Lane, a young man described by other students as extremely quiet, with few if any friends.
The court appearance did little to solve the mystery. Afterward, though, the prosecutor appeared to rule out rumors and speculation that the gunman lashed out after being bullied or that the shooting had something to do with drug-dealing.
"He chose his victims at random. This is not about bullying. This is not about drugs," Joyce said. "This is someone who's not well, and I'm sure in our court case we'll prove that to all of your desires and we'll make sure justice is done here in this county."
Joyce would not elaborate. Both sides in the case are under a gag order imposed by the judge at the prosecutor's request.
Lane's grandfather, who has custody of the teenager, and two aunts joined him in court; the women reached over and lightly embraced the grandfather as the hearing began.
Judge Timothy Grendell ordered the boy held for at least 15 days. Prosecutors have until Thursday to bring charges against him and are expected to ask that he be tried as an adult.
In addition to imposing the gag order, the judge barred media outlets from taking photos of the faces of the suspect and some of his relatives.
The Associated Press transmitted photos and video of Lane that were shot before the hearing. The AP and at least one other media outlet, The Plain Dealer of Cleveland, plans to challenge the judge's order on Wednesday.
Meanwhile, one of two injured students was released from the hospital and shaken residents extended condolences to the families of those killed and wounded at the 1,100-student high school. Grief counseling was offered to students, staff and others at area schools.
"We're not just any old place, Chardon," Chardon School Superintendent Joseph Bergant II said. "This is every place. As you've seen in the past, this can happen anywhere, proof of what we had yesterday."
All three of the dead were students, as are the two wounded victims. The one student still hospitalized remained in serious condition Tuesday evening at Hillcrest Hospital in suburban Cleveland, a hospital spokeswoman said.
The Chardon police chief said authorities learned Tuesday that the wounded female Chardon High student had been released and the 18-year-old was home with her family. He said it is good news amid tragic circumstances.
Authorities said that Demetrius Hewlin, 16, and Russell King Jr., 17, had died. Daniel Parmertor, 16, died shortly after the shooting.
Hewlin attended Chardon High. King and Parmertor were students at the Auburn Career Center, a vocational school, and were waiting in the Chardon High cafeteria for their daily bus when they were shot.
Lane's family is mourning "this terrible loss for their community," Robert Farinacci, an attorney for Lane, said in a statement.
Fifteen-year-old Danny Komertz, who witnessed the shooting, said it appeared that the gunman singled out a group of students sitting together. He said Lane was known as an outcast who had apparently been bullied. But other students disputed that.
Farinacci told WKYC-TV that Lane "pretty much sticks to himself but does have some friends and has never been in trouble over anything that we know about."
Lane did not attend Chardon High but waited there for the bus to Lake Academy, a school for students with academic or behavioral problems. Authorities would not say how and why he ended up at Lake Academy.
Student Nate Mueller said that he was at the table in the cafeteria where the victims were shot, and a bullet grazed his ear. Mueller told The Plain Dealer that King - one of those killed - had recently started dating Lane's ex-girlfriend.
Lane "was silent the whole time," Mueller said. "That's what made it so random."
Kala Day, 18, said she rode the morning school bus with Lane and knew the victims.
"He always sat by himself and like looked out the window. So I sat with him a few times, because I felt bad for the kid. He didn't talk. He just stared out the window," she said.
The shooting sent students screaming from the building in panic, and some of that chaos and fear was captured in 911 recordings released Tuesday.
"We just had a shooting at our school. We need to get out of here. Oh, my god," one crying female caller told a dispatcher.
"Everyone's running away," the caller added.
Another caller, a male student, instantly identified the gunman as Thomas Lane, a student, and said he appeared to be shooting at random.
"What was his beef with these kids? Do we know?" the dispatcher asked.
"I have no idea," he said, adding: "He's very quiet and he doesn't really talk to anyone."
Frank Hall, an assistant high school football coach who has been hailed as a hero by students who say he chased the gunman out of the cafeteria, told a Cleveland TV station that he couldn't discuss what happened, but added: "I wish I could have done more."
AP writers Dan Sewell in Cincinnati; Julie Carr Smyth, Andrew Welsh-Huggins and Ann Sanner in Columbus; and photographer Mark Duncan in Chardon contributed to this report.