The FBI has opened an investigation in a series of threatening letters received by Home Depot stores and Renewal by Andersen businesses in the Twin Cities area, according to an article in the St. Paul Pioneer Press.
A total of 13 letters containing a white powder substance -- which later turned out to be sodium bicarbonate, or baking soda -- were mailed to eight Home Depot stores in Apple Valley, Eagan, Forest Lake, Hastings, Hudson, Inver Grove Heights, Maplewood and Woodbury. Similar letter were mailed to five Renewal by Andersen, a window replacement business, in Bayport, Burnsville, Cottage Grove, Edina and Roseville, the FBI said.
Federal agents gave no information about the content of the letters, which were received between Dec. 31, 2010 and Jan. 6, 2011. The return address on each envelope was identical, and the letters seem to have been photocopied, authorities said.