>> a person's weakest spot is his family, and i'm a rational man. even if i had taken part in an operation, even if i had known what was in the container, would i take my family along? i am a rational man. i couldn't do it. >> reporter: not only did he continue to maintain his innocence, he offered his own theory about who poisoned the tea. could someone have put something in there without you noticing? >> no, why don't you think that the polonium may have been put there into the cup after our meeting the next day or by a guy from mi6? he brings the polonium and pours it into the cup. that's agatha christie stuff. >> reporter: mi6 is british intelligence. lugovoi says perhaps the brits killed litvinenko to embarrass russia. retired mi6 analyst glenmore trenear-harvey says that's nonsense. if for no other reason because mi6 would never use such an expensive weapon to kill anyone.