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CHESTER TOWNSHIP, Ohio (WJW) — An 18-year-old West Geauga High School student accused of bringing a gun to school and developing a plan to shoot multiple students is being held at a secure mental health facility.

Brandon Michael Morrissette, of Lyndhurst, has been charged with felony counts of attempted aggravated murder, illegal possession of a deadly weapon in a school zone and a misdemeanor count of inducing panic, authorities said at a Wednesday briefing.

At about 8 a.m. Monday, a 17-year-old student alerted the school’s resource officer to a bullet found in a bathroom. Authorities reviewed surveillance footage to identify about 20 students who had used the bathroom that morning, each of whom were then interviewed, said police Chief Craig Young.

About an hour later, Morrissette was found to have an unloaded 9-millimeter handgun and three loaded magazines in his backpack, as well as a knife attached to his pants. He was immediately arrested. Young on Wednesday declined to say where Morrissette got the handgun since the investigation is ongoing.

West Geauga schools were then made to shelter in place. Students were sent home later that day. Police later determined there were no additional threats at any of the district schools, Young said.

“During our interview with Mr. Morrissette, he admitted to using prior calculation and design in developing a plan to cause harm to students at West Geauga High School on April 3,” Young said. “He further acknowledged the firearm seized by law enforcement on Monday was the weapon he intended to use to inflict that harm.”

Authorities searched Morrissette’s Lyndhurst home that day, where they found “numerous items of evidentiary value,” the chief said.

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West Geauga Local Schools Superintendent Richard Markwardt thanked the law enforcement agencies that responded to the threat, including police departments in Chester and Russell townships and the Geauga County Sheriff’s Office.

“The potential tragedy was prevented by the collective and concerted efforts by these groups,” he said.

He also thanked district parents for their support.

“It is a sad commentary that schools must face challenges to safety of students and staff, however, it is a reality that we must acknowledge and for which we prepare,” he said. “In reality, every threatening situation has unique nuances that simultaneously require flexibility and decisiveness.

“There is no one-size-fits-all response to a crisis. Monday, our staff and local law enforcement agencies, with the cooperation of our students, successfully navigated such a challenge.”

Young said investigators have not found any evidence that Morrissette was working with other people or that he discussed his plan prior to Monday.

Schools remained closed the following Tuesday because of a second, associated threat discovered on Snapchat, Markwardt said.

Morrissette’s charges were filed in a complaint in Chardon Municipal Court on Tuesday, said Geauga County Prosecutor Jim Flaiz. Morrissette must first be medically and psychologically cleared at the mental health facility before being incarcerated in the county jail, he said.

That evaluation could be finished as early as Friday. He’ll then be taken into custody on a warrant, then formally face the charges in the city court. His case will then be bound over to a grand jury. His felony and misdemeanor charges could change depending on the investigation, Flaiz added.