The woman who mailed letters containing ricin last year to the White House and then-New York City mayor Michael Bloomberg was sentenced Wednesday to 18 years in federal prison.

Shannon Richardson, 36, of New Boston,Texas, admitted that she ordered supplies in her husband's name, made a form of the deadly toxin ricin, sent the letters in May 2013, then told the police she suspected her estranged husband did it. Suspicion turned to her when the statements she made to investigators were inconsistent. The letters sent to President Obama and Bloomberg's New York office were intercepted at off-site mail screening facilities. The letter sent to Bloomberg's gun-control organization in Washington was opened by an official of the group, Mark Glaze, who was not injured.

Her mailings were the second attempt last year to frame someone else for sending threatening ricin letters. In April 2013, a Mississippi man, James Everett Dutschke, addressed letters containing ricin to President Obama, Sen. Roger Wicker, and a Mississippi state court judge. Prosecutors said it was an attempt to blame a rival — an Elvis impersonator named Paul Kevin Curtis. The letters sent to Obama and Wicker were intercepted, but the one to the judge was delivered. It caused no injury. Dutschke was sentenced to 25 years in prison for sending the letters.

IN-DEPTH

SOCIAL