A letter addressed to President Obama that was intercepted after a "suspicious substance" was detected has tested positive for ricin, the same substance found on a letter to Mississippi Senator Roger Wicker yesterday, the Dow Jones news wire is reporting.

In addition, a second letter sent to the U.S. Senate has also tested positive for ricin, according to ABC.

Authorities are said to have a suspect in the case of the letter sent to Wicker—a person who "writes a lot of letters to members," Sen. Claire McCaskill said today. It's also worth remembering that there's a history of ricin false positives that have been used to justify hasty security action.