It started with a single bullet.

A janitor found the .22-caliber round on the ground in Clearview Regional High School's parking lot around 10:20 a.m. Tuesday.

The Mullica Hill school soon went on lockdown. Then came the police K-9's. They sniffed the lot and, later, the building, searching for clues.

The students, who were expecting early dismissal for the holidays, found themselves waiting anxiously for answers.

When they emerged around 12:30 p.m., further investigation followed. Those who drove to school had their vehicles searched so police could determine if anyone had a weapon.

Ultimately, no one did.

"We are sorry for any inconvenience this may have caused to anyone," Harrison Township Police Lt. Ronald Cundey said in a statement. "But the safety of the students and staff is our number-one concern."

Clearview Regional Middle School, across the street, was also locked down as police investigated.

Cundey said there was no threat against the schools. Later, investigators were trying to determine how long the bullet had been in the lot and what gun it came from.

Cundey described the type of bullet as "very common."

"That round will fit in hundreds of different guns," he said.

District officials sent a message to parents around 11 a.m. alerting them of the lockdowns.

mboren@phillynews.com

856-779-3829 @borenmc