Mayor Bloomberg said he feels "perfectly safe" despite letters sent to him and his anti-gun group that were tainted with ricin and hinted of more threats to come.
Bloomberg said on his radio show Friday that threats come with the job. A similar letter send to President Obama is also being tested for the poisonous substance.
"There are legitimate ways to express yourself and then there are ways that just are inappropriate, illegal, disgraceful," Bloomberg said. "I trust the police department and I feel perfectly safe."
Law enforcement officials say a person of interest is being questioned in connection with the letters.
The Texas man is described as an Army veteran who is a contractor with the Department of Defense. He has connections to Shreveport, La., where the letters were postmarked, but is not considered a suspect, several officials said.
The interview with the man is just one possible lead in the case, and officials emphasize the development is still part of the early stages of their investigation.
The threatening letter mailed to Obama was received Wednesday at an off-site facility and did not reach the White House, according to the Secret Service.
"This letter has been turned over to the FBI Joint Terrorism Task Force for testing and investigation," said Brian Leary, a Secret Service spokesman.
The text of the mailings threatened: "what's in this letter is nothing compared to what I've got planned for you," police and law enforcement sources said. A photo of the letter sent to Bloomberg, obtained by NBC 4 New York, is pictured below.
That letter was discovered at City Hall's mail sorting facility at 100 Gold St. on Friday, a law enforcement source told NBC 4 New York. It appeared to contain a 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 more preliminary testing Wednesday showed the letter tested positive for ricin.
An identical letter containing ricin was sent to the Mayors Against Illegal Guns headquarters in Washington, D.C. and was opened on Monday, police said.
According to law enforcement sources, the three similar threatening letters were postmarked May 20 and sent without a return address or signature. Sources said the NYPD tried to pull fingerprints off the letter discovered at the city's mail sorting site, but nothing usable was found. Authorities also plan to check for any possible DNA.
It wasn't known if any viable forensic evidence was discovered on the letters sent to Washington or the White House. All three mailings read in part: "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."
Bloomberg is the founder of the anti-gun group.
On his radio show Friday, he vowed to keep pushing the anti-gun agenda.
"I'll go about my business, and we're certainly going to keep working on getting guns off the streets, out of the hands of criminals and people with mental problems," he said.
Ricin is a poison found naturally in castor beans. Symptoms can include difficulty breathing, vomiting and redness on the skin depending on how the affected person comes into contact with the poison.