Sources tell NY1 that a person is being questioned by authorities in Texas in connection with letters containing ricin that were sent to both President Barack Obama and Mayor Michael Bloomberg.
The U.S. Secret Service confirmed Thursday that a letter sent to Obama is similar to a ricin-laced letter sent to Bloomberg over the weekend.
The agency said the letter intercepted at a federal mail facility last week matches the threatening letter sent to the mayor.
The letter has been turned over to the FBI Joint Terrorism Task Force for testing and investigation.
Bloomberg said he has full confidence in the New York City Police Department and Federal Bureau of Investigation as they try to figure out who mailed him the poisonous parcel.
Speaking to reporters Thursday, Police Commissioner Ray Kelly said the letter was opened Friday at a city mail facility in Lower Manhattan before it got to City Hall.
"These checks in these facilities are in place, and the system worked," Kelly said.
The letter was tested twice.
It also contained disturbing threats.
According to Kelly, its message reads, "Anyone who comes for my guns will be shot in the face."
Three police officers who handled the mayor's letter were treated for minor symptoms and have since recovered.
Another ricin-laced letter was sent to Washington, D.C. and addressed to Mark Glaze, the director of Bloomberg's gun control group, Mayors Against Illegal Guns.
Sources say the letters were postmarked in Louisiana.
"We've always had deranged people threatening public officials, threatening presidents and mayors," Kelly said. "This is not a new phenomenon, but it is something we are concerned about."
Kelly said it is the first time that Bloomberg has been threatened with ricin.
Meanwhile, the city's public advocate has received two threatening letters as well.
Police say Bill de Blasio received two letters in the past few days that appeared to be covered in blood.
Kelly said that both were written in Spanish and sent from the Bronx, and part of the text of the messages read "This is real blood."
Police are now checking to see if that's true.
"There was a letter received by Bill de Blasio on Friday, a threatening letter that appears to have had [alleged] blood on the letter. Then they received another letter, similar letter, apparently from the same person, yesterday," Kelly said.
City police are also investigating two piles of a white substance that were found Thursday in front of a Department of Environmental Protection office at 290 Broadway in Lower Manhattan.
The FBI said if field tests determine traces of ricin or other poisons in a substance, the material is sent to an accredited lab for additional testing. The agency said more letters or incidents could occur.