Suffolk County police on Tuesday were back out at two schools in the Middle Country School District, a day after those schools were briefly under lockout during an investigation into bomb threats.

A police spokeswoman said the department was coordinating with school officials at Selden Middle School in Centereach and Newfield High School in Selden to “ensure the safety of students and faculty.”

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The schools went into lockout mode Monday after notifying police of threats. One threat was made in a fax to the middle school, and that fax included another threat to the high school, according to a statement from the school district.

Newfield High received a threat in a phone call, police said.

Police said they were notified about the threats at 9:57 a.m.; they responded with their canine unit and “nothing was found,” a department spokeswoman said.

By about noon, both schools resumed normal operations, police said.