More than 30 letters containing a suspicious powder were mailed to Chase banks in nine cities, authorities said Tuesday in what was being investigated as a public backlash over the nation's financial crisis.
Initial tests on the powder proved negative for dangerous toxins, the FBI said. An FBI spokesman in Oklahoma, where eight letters turned up, said the powder appeared to be harmless calcium.
Additional tests were run on the letters Tuesday as officials zeroed in on possible suspects near Amarillo, Texas, where the letters were postmarked.
The FBI said in a statement that "even sending a hoax letter is a serious crime."
A law enforcement official said the letters were mailed to Chase bank branches in or near Atlanta; Chicago; Columbus, Ohio; Dallas; Denver; Newark, N.J.; New York City; Oklahoma City; and Washington. They all appear to be from the same source and began showing up at the banks on Monday.
A law enforcement official said authorities were looking into whether the letters were sent in anger due to the economy. Gary Johnson, a spokesman at the FBI field office in Oklahoma City, said that the threat was "based on past actions of the bank" and that the letters implied that the opener was going to die.