According to The New York Times, two letters testing positive for ricin were apparently sent to Mayor Michael Bloomberg and a gun control group he founded late last week. A police officer investigating the letters showed some symptoms of exposure, though that number may have expanded to three.

There aren't yet many details on the letters. One, addressed to Bloomberg, was received at a New York City municipal building at 100 Gold Street. The other was sent to the Washington, D.C., office of Mayors Against Illegal Guns, a group co-founded by Bloomberg which has been central to the recent debate over gun control. Neither address is readily associated with either recipient. The Gold Street building is not where the mayor's office is housed; Mayors Against Illegal Guns doesn't appear to have an easily discoverable address near the capital.

Oren Yavin, a reporter for the New York Daily News, provided updates via the New York Police Department.

Police believe that both letters were sent by the same person.

Last month, ricin-tainted letters were sent to the president, a senator, and a Mississippi judge. Authorities arrested J. Everett Dutschke in that case (after having erroneously arrested Elvis impersonator Paul Kevin Curtis).

Ricin is made from castor beans, and can be created using instructions found online. The Centers for Disease Control notes that the poison is "very toxic," requiring exposure by inhalation or ingestion. Despite that toxicity, deaths from ricin poisoning are rare. The City of New York's Department of Health and Mental Hygiene also has a page of information about ricin.