Most of the letters were in envelopes containing white powder, which so far has tested negative for any dangerous toxins.
But the FBI says the hoax is still a serious crime and it's investigating the letters as a possible extreme backlash to the nation's financial crisis.
"Steal tens of thousands of people's money and not expect reprercussions," says the letter, which is written in all capital letters and includes the misspelling. "It's payback time. What you just breathed in will kill you within 10 days. Thank (name redacted) and the FDIC for your demise."
The FBI would not identify the person whose name was deleted. A U.S. official said the name is a person who may have played a role in the nation's financial crisis, but not a government official. The official spoke on condition of anonymity because he was not authorized to speak publicly.
Authorities said the letters appear to be from the same source, and were focusing on possible suspects near Amarillo, Texas, where the envelopes were postmarked.
The FBI released the text in hopes that the public will help lead investigators to the letter's writer.
Since Monday the letters have been opened in the offices of Chase Bank branches, the FDIC and the U.S. Office of Thrift Supervision, which regulates all federal and many state thrift institutions. They were sent to offices in or near 12 cities: Arlington, Va.; Atlanta; Chicago; Columbus, Ohio; Dallas; Denver; Newark, N.J.; New York City; Oklahoma City; Phoenix; San Francisco and Washington.
An FBI spokesman said letters sent to Oklahoma were filled with harmless calcium.
The U.S. Postal Inspection Service has offered a reward of up to $100,000 for help in arresting the letter mailers.
Authorities "are following several good leads, but we are always looking for more information," said FBI spokesman Rich Kolko. "And we hope that when people see this letter and writing style, it will encourage someone with information to contact the FBI or other authorities."
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