U.S. authorities are investigating a Texas man over threatening letters containing a potentially deadly poison mailed to U.S. President Barack Obama and New York Mayor Michael Bloomberg, a law enforcement official said on Friday.
The probe comes as FBI officials continue investigating a separate batch of ricin-laced letters sent earlier this month from Washington state to the president and four other targets, including the CIA and a military facility.
At this point, investigators do not think the two cases are connected, the source said.
FBI investigators in Texas are questioning a man in New Boston, Texas after his wife called the police to report suspicious activity, the law enforcement source said. The agency is proceeding cautiously, and the man has not been charged, the source added.
Those letters, which media reports said were postmarked from Shreveport, Louisiana, referred to the debate over the nation's gun laws and also were sent to Bloomberg's gun control group in Washington, D.C. Initial tests showed they contained ricin.
In the Washington case, the FBI said Thursday that three of the five letters, including the letter to Obama, have been intercepted and contained ricin.
A fourth letter to Fairchild Air Force Base near Spokane has been located, and a fifth letter to the CIA was detected but not found, the FBI's Seattle office said in a statement.
The letter that has not been located was sent to a CIA location that does not receive mail, the FBI said in its statement.
Authorities have already charged a Washington state man, Matthew Ryan Buquet, for allegedly mailing one of the five letters to a U.S. district judge in Spokane. On Thursday, the FBI said that letter is similar to the other four letters from Washington under investigation.
Mail to top public officials is not delivered directly, but instead goes through off-site screening facilities first. The letter sent to Bloomberg's group Mayors Against Illegal Guns was opened by its director.
Authorities have intercepted several ricin-laced letters in recent weeks. The poisonous substance is found naturally in castor beans but can be converted into a lethal form that can cause death within days. There is no known antidote.
The FBI is moving cautiously after wrongly arresting a suspect in another recent ricin case.
James Everett Dutschke, a Tupelo, Mississippi martial arts instructor, was arrested in April with allegedly sending poison-laced letters to Obama and two other public officials after authorities first arrested another man who worked as an Elvis impersonator.