The FBI said on Wednesday that an investigation into mail containing a suspicious substance addressed to a lawmaker and to President Barack Obama, has not found a link to the attack in Boston.
"The investigation into these letters remains ongoing, and more letters may still be received. There is no indication of a connection to the attack in Boston," the FBI said in a statement.
The envelope addressed to Obama was immediately quarantined by the US Secret Service, the FBI said.
"Only a full analysis performed at an accredited laboratory can determine the presence of a biological agent such as ricin.
Those tests are currently being conducted and generally take 24 to 48 hours," the FBI said.