WILTON, N.H. (AP) – Police on Tuesday locked down Wilton-Lyndeborough Cooperative High School for several hours after a pupil broke open a microscope slide containing dead anthrax.

Hazmat crews sealed off the building and ambulances responded as a precaution and pupils were told to stay in their classrooms.

Administrators were told at 10:50 a.m. about the possible release of a small quantity of a toxic substance. Officials said the slide, about 25 years old, contained a preservative that would kill live bacteria.

About 500 students and faculty were locked in the school between 11:30 a.m. and 4 p.m.

WMUR-TV quoted a student saying that as a prank, a pupil in a science class took the cracked slide apart and rubbed it on other people.

“He was kind of joking around, saying that he was going to give everybody anthrax and stuff like that,” Amanda Pelletier told the station.

The Telegraph quoted a pupil who called the newspaper from his classroom that the slow release of information frustrated many in the building. The student said no one had eaten lunch and everyone had been given only one opportunity to use the toilets.

Parents were left waiting for four hours to pick up their children.

“It’s what parents don’t know that scares them,” said Jeanette Penfield, a pupil’s grandmother. “You need to know what’s going on. You don’t want to just drive up here and see police cars. You’re going to be frightened.”

“It was really scary,” student Tanja Pellerin told the station. “When I heard it was anthrax, I was, like, Oh my God. I just want to go home’ because I know I’m safe there.”

Police Chief Brent Hautanen said it took time to track down the source of the slide and confirm that the anthrax was inert.

All pupils who came in contact with the dead anthrax were told to wash their hands, face, neck and forearms.

Adam Garon, a senior, told the newspaper that at 3:45 p.m. teachers had begun to explain some things after the faculty had not released much information. “They just announced over the intercom they will try to get us out in a half hour, dismiss us one class at a time.

“It’s been a hellish day,” Garon said.