From KPEL :

The Federal Bureau of Investigation is confirming that the first tests done on a letter addressed to President Barack Obama shows the presence of the poison ricin.

Investigators are saying that this point there is no connection between the letter sent to the President and the attack at the Boston Marathon.  Two letters like this one have been sent to U.S. Senators Carl Levin in Michigan and one yesterday to Roger Wicker of Mississippi.

The FBI is said to be questioning a person of interest possibly connected to the suspicious letters sent to President Obama and senators.