andrei lugovoi and dmitry kovtun. in kovtun's case, it was an easy.ew weeks after litvinenko died of polonium poisoning, kovtun was hospitalized and lost all his here. he hasn't been seen publicly since 2012. that left lugovoi. when we got here, he didn't want to speak to us. but on the second day of our trip, he called and said he was ready to talk. >> coming up -- we ask the question the world wants answered. >> did you put polonium in the tea? >> when "dateline" continues. yardwork... teamwork... long walks.... that's how you du more, with dupixent, which helps prevent asthma attacks. dupixent is not for sudden breathing problems. it's an add-on-treatment for specific types of moderate-to-severe asthma that can improve lung function for better breathing in as little as two weeks. and can reduce, or even eliminate, oral steroids. and here's something important. dupixent can cause serious allergic reactions, including anaphylaxis. get help right away if you have rash, shortness of breath, chest pain, tingling or numbness in your limbs. tell your doct