The report says that four of the letters have been examined and were not found to contain any hazardous materials. They are still looking at the other three.

Pete Piringer, a spokesman for D.C. Fire and EMS, says some of the schools were evacuated for precautionary reasons. He says there have been no illnesses or injuries associated with the envelopes and no one has been hospitalized.

The first letter was reported Thursday afternoon at Terrell Elementary School in southeast Washington. They've been mailed to elementary, middle and high schools around D.C.