HAMPDEN – Hampden Academy was “locked down” and after-class activities were canceled Monday after the principal opened a mailed bomb threat.

Two bomb-sniffing dog teams from Maine State Police and the Penobscot County Sheriff’s Department searched the school on Monday afternoon, but no bomb was found.

By 2:30 p.m., a sign on the front door of the school said, “Hampden Academy is in a lockdown. No admittance until 6 a.m. 3/27.”

About 11 a.m., the school’s principal, Ruey Yehle, opened a letter that was addressed to the school without a return address. It was postmarked eastern Maine, according to Emil Genest, assistant superintendent for SAD 22.

The note was printed by hand on a plain sheet of paper and read, “The first bomb will go off at 1:45 p.m. on Wednesday, March 28. The portables [portable classrooms] are safe. Radar.” Genest said the note was signed “Radar.”

Yehle immediately contacted the superintendent’s office and alerted the school’s crisis response team, which includes Hampden Public Safety, the school resource officer and others, Genest said.

Students were dismissed at the usual time, 2:05 p.m., and administrators met with faculty afterward.

Genest said administrators will decide today whether to hold after-school activities tonight as well as whether to have classes on Wednesday.

Someone from the school will monitor the hallways through the night, and Hampden Public Safety has agreed to check the school grounds every half-hour, Genest said.

A meeting is planned with Hampden Academy students at 8 a.m. today, he said.

Contacting parents will be difficult, but the administration was writing a notification for the students to take home to their parents, he said.

“I think there is going to be more anger [from the students] than anything,” Genest said. “Spring sports are just trying out. And if we cancel school we have to make up the day.”

The last day of school is now set at June 15, but a cancellation would force the students to attend classes for an extra day, perhaps a Saturday, he said.