Transcript for Ricin-Laced Letters Sent to NYC Mayor Bloomberg
letters tainted with the lethal poison ricin. Sent to new york city mayor michael bloomberg and his gun control group, abc's brian ross has been tracking it overnight. Reporter: The mayor was never in danger but this morning, officials are treating the two letters as a domestic terror attack and how serious it could have been. Authorities tell abc news, the author wrote the government would never take his guns away and has a god-given right and i will exercise that right until i die, end quote. The letter was stopped blocks away from city hall at a mail screening facility. In terms of why they've done it, I don't know. The letter obviously referred to our anti-gun efforts. Reporter: Authorities said a second ricin letter with identical text wast to the washington, d.C., Office of the mayors against illegal guns. The executive director of the group opened the letter outside on a park bench but told abc news he had no symptoms. Ricin can be a deadly poison but amateurs attempting to use castor beans to make ricin usually produce a much less potent version. If you mail ricin, the intention is going to be you're going to kill somebody or at the VERY LEAST HARM THEM. Reporter: Over the years there have been dozens of ricin letters sent to public officials. Just this spring to the president, a senator and an array of local officials. In all those cases, no one has ever been sickened or died. Mayor bloomberg was defiant when asked if he felt threatened. Were you ago bring -- angry at all? No, I'm not angry. There are people I would argue who do things that are irrational but it's a complex world out there and we just have to deal with that. Reporter: Some of the new york city police officers who handled letters sent here were later examined for minor symptoms of exposure but officials say those have since disappeared and now the effort is to track down who sent the letters postmarked in shreveport, louisiana, on may 20th to see whether there might be more coming. Of course they want to know that. Brian, thank you.
This transcript has been automatically generated and may not be 100% accurate.