So far, no arrests have been made.
The FBI says the letters carried threats to kill their readers within 10 days. The letters accuse the banks of stealing tens of thousands of dollars of people's money. It says to expect repercussions, and to thank the Federal Deposit Insurance Corporation.
The letters also blame a certain person whose name was deleted by the FBI.
The latest news from around North Texas.
So far, the powder accompanying the letters has tested negative for dangerous toxins.
The letter says:
"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 of repercussions.
"It's payback time. What you just breathed in will kill you within 10 days. Thank (-- name redacted -- ) and the FDIC for your demise."