Updated at 7:19 p.m. ET
A letter addressed to President Obama that may have been contaminated with the deadly toxin ricin is similar to two ricin-laced letters recently sent to New York City Mayor Michael Bloomberg, the U.S. Secret Service said Thursday.
A screening facility for mail sent to the White House intercepted the recent letter addressed to Mr. Obama, Secret Service spokesman Edwin Donovan said. The letter has been turned over to the FBI's joint terrorism task force for testing and investigation.
CBS News correspondent Bob Orr reports that the letter was postmarked from Shreveport, La.
Shreveport was also the postmark for the two contaminated letters sent to Bloomberg in New York and his gun-control group in Washington. All three letters were postmarked May 20.
Orr reported Thursday that, according to two sources, the letter sent to Bloomberg carried the following threat:
"You will have to kill me and my family before you get my guns. Anyone wants to come to my house will get shot in the face. The right to bear arms is my constitutional, God-given right and I will exercise that right till the day I die. What's in this letter is nothing compared to what I've got planned for you."
Law enforcement sources say the ricin is crudely made and of poor quality.
Authorities say the three responding officers who came into contact with the letter in New York suffered some minor symptoms. No one was seriously hurt, but the joint terrorism task force, which includes the FBI and the NYPD, is also investigating that case.
Bloomberg spoke with reporters shortly after the threats against him became public Wednesday evening.
"No, I'm not angry," said Bloomberg. "There are people who, I would argue, do things that may be irrational, do things that are wrong, but it's a very complex world out there, and we just have to deal with that."
CBS News correspondent Elaine Quijano reports that a worker at a mail facility in lower Manhattan Friday intercepted the letter addressed to Bloomberg that was laced with the highly toxic poison.
Another tainted letter was discovered two days later in Washington at a building that houses Mayors Against Illegal Guns, a non-profit group Bloomberg helped start. That envelope was addressed to the group's director, Mark Glaze.
Both mailings had no return address.
They contained a pink-orange, oily substance, and each letter threatened bodily harm against the mayor and made references to his stance on gun control.
CBS News correspondent John Miller said that ingesting ricin, even in small amounts, can be deadly. But he added: "What you're seeing here is basically the mashed-up insides of castor beans either into a paste or if it's dried out in a granular form, like salt. What you're not seeing is what we saw in the anthrax attacks where even before you opened the envelope, spores are coming out contaminating the area,and releasing possibly deadly toxins. So to frame this, it's not as dangerous as what we've seen before."
Last month, a Mississippi man was arrested for trying to send ricin-laced letters to Mr. Obama, Mississippi Sen. Roger Wicker and a judge. The letters addressed to the president and Wicker were sent April 8. Both letters tested positive for ricin but were intercepted before they reached their targets.
James Everett Dutschke was arrested at his home in Tupelo, Miss., April 27 in that investigation. In court papers, the FBI said ricin was found in a martial-arts studio run by Dutschke.
After these series of recent events pertaining to ricin, what could be expected next? Miller said that the people who are sending these letters are doing it for two purposes: "One, to threaten and intimidate the person it's addressed to--in this case, Mayor Bloomberg, the president, members of Congress. But the other is to get publicity and to do that for their cause.
"So what you're going to see is a serious discussion between authorities -- but also within our own newsrooms -- because the more attention these get, that usually means the more of these incidents we're going to see in the future. And the discussion will have to be about how much attention we want to give to these stories."