WASHINGTON — Over the past two months, authorities have seized a succession of letters laced with the toxin ricin intended for the CIA, President Barack Obama and other public officials.
Viewed as "copycat" events by some investigators, the letters have generated high-profile coverage on television and were widely reported by other media organizations, including the nation's major newspapers.
But experts say the ricin that has been sent through the mail has posed little health risk for two reasons.
One is that considerable laboratory expertise would be needed to purify, concentrate and dry the toxin in a way that makes it potentially lethal by inhalation. And, compared to another feared bioterrorism agent, anthrax, ricin is not nearly as toxic when released through the air.
Not a single person exposed to ricin sent through the mail this year — or ever, authorities say — has died or been found by doctors to have been sickened by it. According to Bioterrorism, a 2012 book edited by microbiologist Steven Morse of U.S. Centers for Disease Control and Prevention, "There are no documented cases." However, it warned, "... its potential as a weapon of terror cannot be discounted."
What distinguishes ricin from other Category B bioterrorism agents listed by the CDC is that it is easily obtained. All that a would-be terrorist needs to get started is to buy or harvest castor beans, which contain the toxin.
On Wednesday, the New York City Police Department said in a written statement that three male officers who dealt with one of the recent letters — addressed to Mayor Michael Bloomberg — were "being examined for minor symptoms of ricin exposure."
But on Friday, a department spokesman, Paul Browne, acknowledged that extensive hospital testing of the three had found no sign of ricin in them.
Separate tests by the National Bioforensic Analysis Center in Frederick, Md., found only minute concentrations of ricin in the letters addressed to Obama, Bloomberg and a Washington, D.C.-based gun-control organization affiliated with the mayor, according to people familiar with the matter.
Referring to the tests of the ricin letters to Bloomberg and Mayors Against Illegal Guns, Browne said: "The national lab had told us that the ricin was crude and low-level, crudely produced. This looks like somebody who may just have smashed up a bunch of (castor) beans."
In the investigation of the letters sent to Obama and Bloomberg, a Texas home was searched and a resident interviewed on Friday, a law enforcement official said.
Authorities blocked off the house in New Boston for hours and set up tents in the yard while searching for evidence.
The FBI initiated the search after being contacted by the resident's spouse. No suspects have been named.
Information from the Associated Press was used in this report.