On the eve of Halloween, officials at Mount Vernon High School were forced to dismiss students early after someone pulled the fire alarm three times.

"It's one day before Halloween, mischief night, so we think it's part of a prank," says District Spokesperson Desiree Grand.

The alarms went off at around 1 p.m. Thursday afternoon. Although school administrators suspected the incident was a pre-Halloween practical joke, they had to respond like it was a real emergency, Grand says.

All the students were evacuated from the building after the first alarm went off, and police and firefighters arrived at the scene. When students were allowed to return to their classrooms, a second alarm sounded. School administrators decided to dismiss students at 2 p.m., about half an hour before the end of classes.

Officials say they will review surveillance videos throughout the weekend in order to determine the identity of the Halloween prankster.