It all seemed like a lockdown drill to Cherry Hill East students, until that lockdown turned into an evacuation past police and bomb-sniffing dogs, after a threatening message was left in a bathroom at the high school Monday.

Rumors of a possible bomb threat—school officials didn't elaborate on the nature of the threat, only that it had been written in a bathroom—circulated by text and on Twitter almost immediately after the lockdown happened around 1:30 p.m., but students said it didn't seem real until they started streaming out of the building to find eight police and sheriff's cars and SUVs parked on the sidewalk, dogs growling from darkened interiors. "That caused me to go to panic," said Freya Thanner, a junior at the school.

Before then, it seemed like one of the regular drills at the school, which didn't throw off students, who hunkered down in their classrooms to wait for more information during what was labeled a Tier 2 lockdown—which includes bomb or other weapons threats. Some teachers continued their classes as normal, students said, but as the lockdown dragged on toward 25 minutes, things started unraveling. "We're no strangers to lockdowns," senior Aleks Brittain said. "What was odd was that it happened 10 minutes before the period ended. It usually happens a lot earlier."

If that was their first clue, an announcement by one school administrator telling everyone in the building to ignore the bell at the end of the period was the clearest message, students said. "That was when we all realized, 'This is not a drill any more,'" Brittain said. "There was no one in the halls at all, and none of our teachers would let anyone out."

After about 25 minutes of lockdown, administrators came on the intercom again to give the order to get out—students said they were told to head straight out of the building and not go to their lockers; teachers were to stay five minutes beyond that, then get out, as well.

Dozens of students were already making the hike down Kresson Road to adjoining neighborhoods as the school began emptying just after 2 p.m., while their classmates piled into cars and buses to get off the campus.

Police and staff directed the buses en masse out of the school's exits on Kresson, as officers checked to make sure everyone had left the building and prevented anyone from going back inside. Several police and sheriff's officers were in the building even as students left. "It all happened very fast," Brittain said.