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.
Chief New York Police spokesman Paul Browne said that threats in the letters contained references to the debates on gun laws. When asked if the letters had anything to do with his outspokenness about guns, Mayor Bloomberg said he didn't know.
"In terms of why they did it, I don't know," Mayor Bloomberg said. "The letter obviously referred to our anti-gun efforts, but there's 12-thousand people that are going to be killed this year with guns and 19-thousand are going to commit suicide with guns and we are not going to walk away from those efforts.
Bloomberg is one of the nation's most prominent gun-control advocates.
"And I know I speak for all of the, close to a thousand mayors in the mayor's coalition against guns - this is a scourge against the country and we need to make sure that we get under control," he said.
This follows a scare March, when ricin-laced letters were sent to President Obama and other politicians.
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.