The FBI is investigating six additional letters containing a white powdery substance that were sent to D.C. schools and received Friday morning, after at least 29 similar letters were recovered on Thursday.
Investigators from the Washington Field Office are working with D.C. police and fire officials and the U.S. Postal Inspection Service to look into the letters. No hazardous substances were found in the mailings and no one has been harmed, officials said.
Schools began reporting that they had received the letters around midday Thursday. The addresses were printed, not handwritten, and addressed to a school and not an individual, the FBI said.
The FBI said each item will be analyzed by an approved regional lab before it is transported to the FBI's Laboratory at Quantico, Va.
"Experts there will perform a variety of tests in an effort to determine who sent the letters and whether the letters are linked to any other pending investigation," the bureau said in a statement.
Authorities think the letters were sent from the Dallas area and "are similar in style and content to other suspicious letters under investigation by Dallas FBI and U.S. Postal Inspectors." The materials are also similar to letters received at D.C.-area schools in October 2010, according to the FBI.
There has been no indication the suspicious letters are connected to word of Osama bin Laden's death, as the letters were already in the mail at the time of the announcement, an FBI spokesman said.
Schools that received letters on Friday morning are: Bancroft Elementary School and Dunbar High School in Northwest, Anacostia Senior High School in Southeast and Drew Elementary School, Prospect Learning Center and the Choice Academy at Brentwood Parkway in Northeast.
Mayor Vincent C. Gray has called the mailings "a dastardly act."
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