DALLAS (AP) -- Federal agents are trying to track down who used various Dallas post offices to send suspicious letters to governors in Missouri, Alaska and other states.
The FBI says those envelopes contained a white powder that was later determined to not be dangerous.
FBI Special Agent Mark White in Dallas says it's possible more letters could arrive in the next few days, since it can take time for them to go through the mail.
The governors' offices in Alabama, Alaska, Michigan, Minnesota, Mississippi, Missouri, Montana and Rhode Island received the letters. The FBI says governors' offices in all other states have been warned to be on the lookout for suspicious letters.
Tests showed the powder was not dangerous, but officials are still trying to determine what it was.
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