Students evacuated Gray-New Gloucester Middle School on Tuesday in response to a bomb threat.

The Cumberland County Sheriff’s Office and Maine State Police responded to the school on Libby Hill Road in Gray shortly after 11 a.m. Tuesday. Several students reported finding a bomb threat written in the boy’s bathroom of the eighth-grade wing of the school.

SAD 15 Superintendent Craig King said in an email early Tuesday afternoon that all 600 middle school students evacuated to the high school while the threat was investigated. Deputies from the sheriff’s office and two K-9 teams from the Maine State Police searched the building. They did not find any explosives. The building was declared safe and students returned to the middle school by 1:20 p.m.

“We had a viable threat,” King wrote in the email. He did not respond to an email with follow-up questions.

Capt. Scott Stewart said the Cumberland County Sheriff’s Office is investigating the incident.

Since the Valentine’s Day school shooting in Parkland, Florida, that killed 17 students and teachers, there have been more than a dozen threats against Maine schools. More than 10 teenagers have been charged in connection with those threats.

A 13-year-old Gray-New Gloucester Middle School student was charged with terrorizing earlier this month after allegedly writing a bomb threat in a school bathroom. A threat about the school “getting bombed” was found written on a bathroom stall March 7, prompting an evacuation of all students and staff to the high school. The sheriff’s office and state police searched the school with two explosive-detecting dogs. No explosives were found. The teenager who was charged was not identified.