The deadly poison ricin has been detected in a letter addressed to New York Mayor Michael Bloomberg, as well as in a second letter addressed to the Washington, D.C., offices of the Bloomberg-backed Mayors Against Illegal Guns, reports the New York Times.
This follows a scare March, when ricin-laced letters were sent to President Obama and other politicians.
In the March incidents, a suspect was wrongly charged before a new suspect was named.
Ricin, an extremely lethal substance derived from castor oil plant, became a household after it was featured as a mode of assassination on Breaking Bad.