CHARDON, Ohio — Prosecutors on Thursday formally charged a 17-year-old with murder in a school shooting rampage that claimed three students’ lives.

T.J. Lane will have a hearing next week before a juvenile court judge in Geauga County to determine whether he will be charged as an adult. As a juvenile, he is ineligible for the death penalty.

Prosecutors have said that Lane, who attended a school for at-risk students, confessed to randomly firing on a group of students at Chardon High School in Chardon on Monday morning, but his motive is unclear. Two students were wounded, and a third was grazed in the ear by a bullet.

Frank Hall, an assistant football coach whom police credited with chasing Lane out of the school after the shootings, spoke publicly about the shootings for the first time Thursday.

“I don’t know why this happened. I only wish I could have done more. I’m not a hero. I’m a football coach and a study hall teacher. Law enforcement, first responders . . . they are the heroes,” Hall said, his voice choked with emotion.

Authorities said classes will resume Friday.

About 50 Chardon students gathered Thursday in the city’s downtown, where they held hands and sang the school song around a pavilion decorated with red ribbons, candles, flowers and stuffed animals.

The crowd soon swelled to about 1,000, and the group walked past flags flying at half-mast to the school, where Superintendent Joe Bergant hugged every student who entered. Grief counselors were on hand to speak with them.

“This is a defining moment for us,” said an 18-year-old student named Brandon who declined to give his last name. He said he was mostly worried about re-entering the school cafeteria, where the shootings occurred.

Lane has told police that he took a .22 caliber Ruger pistol and a knife to the school on Monday and randomly fired 10 shots into a group of students sitting at a table, according to prosecutors.

Daniel Parmertor, 16; Demetrius Hewlin, 16; and Russell King, 17; were killed. Nick Walczak, 17, remains in serious condition in a hospital with neck and back injuries, and another student has been released from the hospital.

Lane was charged with three counts of aggravated murder, two counts of aggravated attempted murder and one count of felonious assault.