Classes were dismissed early Friday at a central Pennsylvania school where a single bullet was discovered in the building.
Officials said they didn't find a weapon at Manheim Township High School.
According to a district statement, the school was placed on lockdown Friday morning after the bullet was found on the floor of a classroom.
Administrators said they worked with police to investigate, including searching the room and interviewing students.
Officials determined there was no immediate threat, but still don't know where the bullet came from.
Students were released at 12:30 p.m.