A 16-year-old student allegedly shot and killed a 15-year-old boy during an “altercation” in the boys’ restroom at Joppatowne High School in Joppa, Maryland, on Friday, authorities said.

The 15-year-old was cared for by school nurses and the principal and then flown by helicopter to a trauma center, where he is in serious condition, Harford County Sheriff Jeff Gahler said at a news conference.

The 16-year-old suspect left the school and fled to nearby homes, the sheriff said. Thanks to the help of community members, he was arrested “within minutes,” Gahler said.

The shooting occurred on the suspect’s first day at the school, but the new school year began four days ago, Gahler said.

Apparently a shot was fired during the incident, the sheriff said, noting that the weapon has not been found.

Authorities do not know what the apparent argument was about, the sheriff said.

The suspect is known to authorities and police have previously responded to emergency calls related to the teenager, authorities said.

More than 100 police officers arrived at the scene in Joppa, about 35 miles northeast of Baltimore, Gahler said.

“We are just devastated to be part of this horrific group of schools that experienced something like this,” said Sean Bulson, superintendent of Harford County Public Schools. “And we will do everything we can and work with this community to make sure that absolutely nothing like this happens again.”

The school does not have metal detectors, officials said.