Federal authorities are investigating whether letters delivered to two dozen D.C. schools Thursday were mailed by the same “dastardly” individual who has been terrorizing institutions across the country. James McJunkin, the assistant director for the FBI Washington Field Office, said the letters were similar to those sent to District schools in October, but they could have been mailed by a copycat.

“We do not characterize it as a prank,” McJunkin said. “What they have done is commit a serious criminal offense.”