( CNN ) -- The FBI found `` very low concentrations '' of ricin on letters sent this week to President Obama , New York Mayor Michael Bloomberg and a gun control group , a spokesman said Friday . Mayors Against Illegal Guns was founded by Bloomberg . FBI spokesman Christopher Allen said lab results showed small amounts of ricin on the three letters . Meanwhile , in what appears to be a separate incident of possibly poisoned mailings in Washington state , the FBI confirmed the presence of ricin on a letter sent to Fairchild Air Force Base near Spokane , the agency said . One front of the FBI investigation advanced Friday in Texas , where authorities searched the home of a man in New Boston in connection with the threatening letters to Obama and Bloomberg . FBI agents interviewed the man after his wife contacted authorities , saying she had found suspicious containers in their New Boston home , two law enforcement officials with knowledge of the investigation told CNN . One of the two officials , who spoke on condition of anonymity , said there were questions about what the man 's wife told authorities . `` We 're looking at the credibility of the complainant and using due diligence , '' the official said . Both sources told CNN that the wife told authorities she found a suspicious container and ricin research on their computer . Word of the search in Texas comes a day after the FBI said its agents were looking for a letter sent to the CIA that they believe is similar to other letters , mailed from Spokane , Washington , that contained the deadly toxin . In all , at least 10 ricin-laced or suspected ricin-laced letters have been sent to government officials in recent weeks , including Obama . CNN 's Mariano Castillo contributed to this report .
It was found on letters sent to president , New York state , animal control group . In a separate incident , ricin is also found on letter to military base . FBI on letter sent to the CIA .