On Monday, October 13, five Chase banks in Colorado and Oklahoma were sent threatening letters that contained a white powder. In all, at least 30 threatening letters were sent and each letter contained an unidentified powder. The FBI, Postal inspectors, and local authorities have been investigating this powder. However, field tests on this powder are negative for harmful substances but more labs will do more testing. Whoever sent the letter or what the powders are, is still unknown.
Source:http://www.comcast.net/articles/news-general/20081021/NEWS-US-USA-CRIME-BANKS/