Police dogs swept the school to make sure no other devices are on school grounds.

QUINCY — Officials are reviewing school surveillance footage to try to figure out who brought a small used smoke bomb into North Quincy High School, prompting an evacuation and early dismissal Monday.

Quincy Public Schools Superintendent Richard DeCristofaro said at a press conference that he decided to have students dismissed after a teacher found the "micro smoke device" in the school library around 9:30 a.m. Firefighters were called to the school and police officers with dogs swept the building in search of additional devices.

DeCristofaro said the device, which was of a type typically used in paintball games, had already been set off before it was brought into the school. No other devices were found.

"There was never any real danger to our staff or students," DeCristofaro said. "We do a lot of training with the Quincy Police Department and our dogs all during the summer and our breaks."

DeCristofaro said police swept the school for several hours Monday. The school was cleared by officials Monday afternoon.

North Quincy High School was scheduled to have a regular school day Tuesday.

DeCristofaro said officials do not know who left the smoke bomb in the library but said authorities are reviewing surveillance video to find the culprit.

North Quincy High has about 1,400 students.