Andrew Mollenbeck, wtop.com

WASHINGTON – For the fourth consecutive day, letters containing suspicious white powder arrived at locations in D.C., including an elementary school.

The FBI confirms multiple such letters on Thursday alone. One envelope went to the Amidon-Bowen Elementary School at 401 I Street in Southwest. The other arrived at the restaurant Bibiana near 12th and H streets in Northwest.

Each letter was field-tested and determined to be non-hazardous.

Investigators believe they are related.

On Wednesday, Adams Elementary School off 19th Street was evacuated after a similar letter arrived. Three people were exposed to the powder, but no one at the school showed any symptoms.

Other packages were also reported that day at Oyster Elementary School and at the Willard Intercontinental Hotel on Freedom Plaza.

Officials are also looking into 20 letters sent to locations throughout the U.S. this week, including New York, Dallas and Connecticut.

Since 2007, an unknown sender has distributed 360 letters to various government officials and public schools, a federal law enforcement source says.

That includes a series of letters sent to local public schools last May.

In late February, congressional offices outside the Beltway received suspicious packages. Sen. Pat Toomey got one in Philadelphia Feb. 23. No injuries were reported.

The FBI has not linked the recent D.C. letters to those sent outside the capital region.

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