A week ago Thursday, Shannon Guess Richardson traveled from her small town in Texas to meet with investigators in Louisiana and accuse her husband of a disturbing crime. Ms. Richardson, a pregnant mother of five, said she suspected that her husband, Nathaniel, had mailed three ricin-laced letters to President Obama, Mayor Michael R. Bloomberg of New York and a gun-control lobbyist in Washington. She also offered hard evidence: a book of stamps that microscopic analysis revealed to be the source of the stamps on the three letters.

But on Friday, the Justice Department said that it was Ms. Richardson herself, an actress with several small television and film credits, who had been arrested and charged with mailing a threatening letter to the president of the United States. A criminal complaint suggested evidence of a frame-up.

If so, it was the second time in two months that a local grudge had spun out of control, and onto the national stage, with ricin-laced letters addressed to the White House.