WASHINGTON (WUSA) -- The FBI confirms suspicious envelopes were found at a total of six schools DC schools Friday morning.
Another four envelopes were intercepted by the U.S. Postal Inspection Service at post offices and a postal processing facility before they could get to schools, officials said.
Investigators suspect the mailer may have been doing this kind of thing for years. Postal Inspectors in Dallas are offering a $100,000 reward for information leading to the arrest and conviction of the man who sent similar letters to the Governors of North Carolina and Connecticut.
Law enforcement sources tell 9NEWS NOW the suspect may have sent out 275 letters to schools, hospitals, governors and federal agencies across the country.
DC Fire and EMS officials confirm units have been called to: Prospect Learning Center at 920 F Street in Northeast, Bancroft Elementary School on Newton Street in Northwest, Drew Elementary School at 5600 Eads Street, Northeast, Dunbar High School in Northwest, Anacostia High School and Hamilton Junior High School.
None of the envelopes at those locations was found to be hazardous.
The FBI has not confirmed the substance in the envelopes. The powder is being tested in an FBI lab.
Thursday, DC Fire and EMS, DC Police, and the FBI were called to 29 schools for reports of suspicious letters.