A letter sent to Mayor Michael Bloomberg at a city building last week contained a substance that has preliminarily tested positive for ricin, police said.
The letter was discovered at the city's mail sorting location at 100 Gold St. at about 2 p.m. Friday, a law enforcement source told NBC 4 New York. It appeared to contain a kind of pink, oily substance when a mail worker came across it and was immediately flagged as suspicious.
An initial field test didn't bring up any sign of ricin, a source said. But further testing Wednesday showed the letter preliminarily tested positive for ricin.
A second letter containing ricin, apparently from the same person, was sent to the Mayors Against Illegal Guns' headquarters in Washington, D.C. and was opened on Monday, police said. Bloomberg is the founder of the coalition.
The letters' author threatened Bloomberg, referring to his stance on illegal guns, police said.
Both letters were postmarked May 20 in Shreveport, La., a law enforcement official said.
Civilian workers who came into contact with the letters have not shown symptoms of being poisoned by the ricin, police said. Some members of NYPD's emergency service unit who did come into contact with the opened letter in New York initially showed some minor symptoms of ricin exposure, but they have since abated.
The FBI and NYPD are investigating the threats. Law enforcement officials are also looking to see if other similar letters were sent to the White House, members of Congress or other government offices as a precaution.
Ricin is a poison found naturally in castor beans.
It's not clear if the letters were related to other threatening, ricin-laced letters sent to other lawmakers recently.
Photo Credit: NBC 4 New York