A security guard spotted a man on the roof of a Medford elementary school early Thursday evening as about 30 children attended an after-school program inside, Suffolk police said.
The children at the Tremont Elementary School were moved to a secure area as officers and a K-9 unit searched for the man, police said.
But a review of video footage showed he had not gone inside the school but ran away outside, police said.
The incident started about 5:30 p.m. when police received a 911 call about a suspicious male on the roof. The security guard tried to talk to the man and went to a door to confront him, police said, but lost sight of him.
Officers stayed with the children in the secure area and the students were not alarmed by the activity, police said.
The suspect, who wore a gray, hooded sweatshirt, was not found, police said, but the investigation continued into the night.