maduro did refer to several u.s. citizens who had been arrested allegedly involved in recruiting venezuelans or in espionage activities. we don't know their names, of course or their identities. >> phil gunson thanks for your expertise. also juan carlos lopez. of course we have a lot of news to get to including out of moscow. brand-new video that may show the murder of an outspoken krit ek of vladimir putin. boris nemtsov was shot four times in the back just yards from the kremlin. he and a female friend were walking home from dinner. shots rang out as they crossed a bridge. our matthew chance is standing on that very bridge. you can see in some surveillance video we'll show you in just a moment. what do we know about this hour in terms of putin and the government's response to this?