A school in Rockland County was evacuated twice Friday after two separate bomb threats were found on the premises, officials say.

North Rockland Superintendent Brian Monahan says officials at Fieldstone Secondary School in Thiells saw a note in the school building suggesting there was a bomb. Following the discovery, all 1,200 students were evacuated to Willow Grove Middle School.

The Rockland County Sheriff Department's bomb unit conducted a search at the school Friday morning, which yielded no traces of explosives, and the students resumed class. However, shortly before the end of the school day another note was found at Fieldstone.

"The building has once again been searched, and again nothing has been found," Monahan says. "We're taking this very seriously. This is obviously a troubled individual who is doing this."

Monahan adds that school officials are working with Haverstraw police to determine who wrote the notes.