A police officer doing a routine check of the new Sanford High School early Monday morning found a small fire in the lobby that school officials say could push back the opening of the building.

The lobby fire, which did not spread, was one of three small fires discovered inside the school building, which is under construction and slated to open to students in September. The person or people who broke into the building used blue prints, ceiling tiles and construction debris to fuel the fires, said Superintendent David Theoharides.

Police believe the fires were set sometime between midnight and 4 a.m. A police officer checking on the building at 4 a.m. saw a glow in the front lobby and called the fire department, Theoharides said.

Firefighters found another small fire near an elevator down the hallway from the lobby and a third near the gymnasium. Both of those fires had already burned out, Theoharides said. Theoharides said someone also broke a large window on an office currently being used by contractors and drove a scissor lift through the science and technology wing, damaging some metal studs. The damage is still being assessed, but Theoharides does not believe it is extensive.

The building is currently being treated like a crime scene and construction crews were sent home for the day. The state fire marshal has been called to the building to investigate.

Theoharides said he worries the vandalism and construction delay could push back the opening of the $100 million high school and regional technical center. The project is the most expensive school construction project in Maine history.