(NEW YORK) -- New York City police say two verbally poisonous letters sent to Mayor Michael Bloomberg contained traces of actual poison: ricin. The author of the letters, police say, targeted Bloomberg because of his support for gun control measures.
One letter was sent to New York, the other to the Washington, D.C. office of Mayors Against Illegal Guns. Police and the FBI are now investigating the anonymous letters, the author of which threatened Bloomberg and mentioned the national gun control debate. The New York City mayor has joined that debate, voicing his support for reform and calling for background checks and a ban on assault-style rifles.
Ricin is a highly toxic poison that comes from castor beans. "It's the leftovers of what castor oil is made from. It can cause death within 36 to 72 hours," explains ABC's Dr. Jay Adlersberg.
"When ricin gets inside of the cells of a person's body, it prevents the cells from making important proteins that can cause cell death and organ failure," he says.
Mayor Bloomberg referenced the threatening letter Wednesday night as he walked into an event in Manhattan.
"There was a letter that threatened us and let me tell you number one I have enormous confidence in the NYPD and the FBI and their procedures. We take a lot of security measures as you know. The men and women that open the mail for example -- they are well trained and we have procedures for something like this. This was not the first letter that was sent to anybody," Bloomberg said Wednesday night. "In terms of why they did it -- I don't know -- the letter referred to our anti-gun efforts."
Bloomberg added that with thousands of Americans who will die as a result of guns, "we are not going to walk away from those efforts. I speak for close to [a thousand] mayors in the effort against gun violence -- this is a scourge against the country and we need to make sure to get this under control."
A reported then asked Bloomberg if the poisoned letters made him feel threatened. He replied, "No I do not feel threatened."
"Are you angry?" the reporter asked.
"No I'm not angry. There are people that do things that might appear irrational -- things that are wrong. But it's a complex world out there. And you just have to deal with that," Bloomberg said.
Copyright 2013 by ABC News Radio.