All students and staff at the Mattituck-Cutchogue junior and senior high school were evacuated from the building for about two hours Thursday morning.
The students were led outside after a “disturbing image” was found in a bathroom, said Police Captain Martin Flatley.
The image, a hand-drawn grenade, was spotted on a girls’ bathroom wall.
“It was an image the school administration believed warranted a check of the building,” the captain said. No suspicious materials or packages were found.
The school campus was cleared at about 10 a.m. with students sent either to the front lawn or the tennis courts off Pike Street, which was closed. A Mattituck Fire Department truck and crew was on standby while police investigators searched the building.
Students were let back into the building at around noon.