The incident occurred at Notre Dame High School in Fairfield around 1 p.m., Thursday, April 11.
According to Sgt. Michael Stahl of the Fairfield Police, the school received a telephone threat of violence and notified the police.
The school was placed into lockdown while officers completed an assessment of the threat and determined that all students and staff were safe, Stahl said.
"At this time, we believe this to be a swatting incident and that the call to the school was not made from the immediate area," Stahl said.
The lockdown was lifted, and school operations, including dismissal, resumed as scheduled.
Fairfield Police will remain on scene through dismissal and are actively investigating the source of the phone call.
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