(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.
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Ricin was found on letters sent to president, New York mayor, gun control group
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In a separate incident, ricin is also found on letter to military base
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FBI seeks letter sent to the CIA
FBI agents interviewed the man after his wife contacted authorities, saying she had found suspicious containers in their New @placeholder home, two law enforcement officials with knowledge of the investigation told CNN.