President Obama was the intended recipient of a letter suspected of containing the poison ricin, following similar letters sent to New York Mayor Michael Bloomberg, law enforcement officials told ABC News.
The letter was intercepted at a White House sorting facility and never reached the President. It has been taken to a lab for further testing, the officials said.
NYPD Police Commissioner Ray Kelly told reporters today he believes that letter is identical to a pair of letters recently sent to Bloomberg that were suspected of containing ricin, as revealed by police Wednesday. Earlier today, the Secret Service confirmed the apparent link between the letters.
The full text of the letter, according to a source briefed on the law enforcement probe, reads, "You will have to kill me and my family before you get my guns. Anyone wants to come to my house will be shot in the face. The right to bear arms is my constitutional God-given right and I will exercise that right 'til the day I die. What's in this letter is nothing compared to what I've got planned for you."
Kelly also revealed that another letter with a suspicious substance was sent to a Environmental Protection Agency office in New York but officials have not determined what the substance is.
Late Wednesday, NYPD spokesperson Paul Browne said a pair of letters had been sent to offices connected to Mayor Bloomberg in New York and in Washington, D.C. Neither of the letters reached the mayor.
The letters – with identical text -- were printed from a computer and are postmarked May 20 from Shreveport, La.
Early this morning, Shreveport Mayor Cedric Glover said his city is working with the FBI and the Joint Terrorism Task Force to "apprehend those responsible for mailing ricin-laced letters to New York Mayor Michael Bloomberg."
"We are also taking the necessary steps to protect local [Postal Service] and Government Plaza personnel as well as local citizens from any possible harm," Glover said.
One letter was sent to Bloomberg at City Hall in Manhattan. The other was dispatched to the director of Bloomberg's organization, Mayors Against Illegal Guns, in D.C. Browne said preliminary tests on that letter showed it also appeared to contain ricin, though the Washington police report of the incident said that "no hazmat (hazardous) material was found."
Bloomberg, a billionaire who has long crusaded for stricter gun control around the country, responded with a flash of defiance.
"No, I do not feel threatened," the mayor told reporters last night. "This was not the first letter that was sent to anybody. In terms of why they did it - I don't know - the letter referred to our anti-gun efforts. There are 12,000 [people] that are going to be killed this year with guns and 19,000 are going to commit suicide by guns and we are not going to walk away from those efforts."
"I speak for close to 1,000 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," he added.
Asked if he was angry, Bloomberg said he wasn't.
"There are people that do things that might appear irrational - things that are wrong," he said. "But it's a complex world out there. And you just have to deal with that."
One Bloomberg insider told ABC News the mayor himself made the decision to go public with news of the ricin-laced letters as soon as a second, more reliable round of tests returned positive results for the poison.
Boston's mayor, Thomas Menino, a co-director at Mayors Against Illegal Guns, said that Bloomberg was "marked because of his position, and my position, on illegal guns."
"This is not going to stop us. They can make all the threats they want," Menino said today.
At its most dangerous ricin can kill, though it is quite difficult to deliver a dose that intense. The toxin, which comes from castor beans, stops cells from synthesizing proteins so victims can suffer organ failure.
Ricin is relatively easy to make with recipe instructions available online. Experts do caution that people trying to concoct the toxin on their own risk poisoning themselves.
Past Ricin Threats
Last month, ricin-tainted letters were sent to President Obama and to government offices, including that of Sen. Roger Wicker, R-Miss.
The letter addressed to the president was received at the White House mail facility and included the message "To see a wrong and not expose it is to become a silent partner to its continuance."
The Senate mail facility received the letter addressed to Wicker. It contained the same message.
A ranking counter-terrorism official in New York marveled at how ricin has become so popular among those trying to scare of harm others more than 11 years after anthrax-tainted mail terrified a nation still reeling from the 9/11 attacks.
"Instead of the drug of choice, it [ricin] has become the weapon of choice of people who might be thinking that," the official said.
One Bloomberg letter was opened by screeners at the City Hall mail facility a few blocks from the building on Gold Street, in Lower Manhattan. Bloomberg's aides said the episode proves the counter-terror measures in place at City Hall worked because no unscreened or suspicious mail gets to the mayor, his staff or anyone else who works in the building – including the press corps.
The second letter was sent to Mark Glaze, director of Bloomberg's group, which has its offices in Northwest Washington, near the White House. Glaze actually opened the letter himself on a park bench and then called for help after seeing the powder in the envelope, a source told ABC News. He declined to comment.
A D.C. police report obtained by ABC News said Glaze found the envelope to contain "a threatening message which had a whitish orange substance on the note…The letter was addressed to [Glaze] but there was no return address or sender's name."
ABC News' Josh Haskell contributed to this report.