On April 15 , 2013 , an envelope that preliminarily tested Testing positive for ricin , a highly toxic protein , was intercepted Preventing_or_letting at the US Capitol 's off-site mail facility in Washington , D.C .

On April 17 , 2013 , an envelope addressed Expressing_publicly to President of the United States Barack Obama preliminarily tested Testing positive for ricin .

The letters tested Testing positive for ricin during FBI testing Testing .