Since the U.S. has been trying to destabilize and destroy Venezuela for the last 20 years (apart from the 200 years of Monroe Doctrine where we constantly fuck over Latin America because we can), and since the only countries that have successfully assassinated people with drones are the U.S. and Israel (otherwise it's been terrorists we fund and arm), it's almost certain that if the U.S. government isn't behind this it definitely had a part in it.
There no question about the history of the Monroe doctrine and the using it to justify screwing over large swaths of South America, and along with that, a whole host corporate abuse and exploitation are well known. Further sense the death of Hugo Chavez and the fall out of the oil market pretty much no country in South America has suffered as much as Venezuela (Maybe with exception of various gang wars), the average national weight lose to due poor nutrition alone is simply such a telling figure. Certainly US trade/Foreign policy hasn't helped in that regard. That said, US drone technology is almost certainly the best in world. two+ washing machines sized drones packed with explosives (New reports vary on the number) strongly suggest some amateur group, probably internal. US combat drone aren't typically seen and they don't blow up their target by being washing machine sized and packed with explosives. Further assassinating a foreign leader who has been as inept as Maduro doesn't make any sense. The guy had the lowest election turn out in Venezuelan history. It has been suggested this was false flag operation developed to justify further internal repressive action take in the wake the supposed attack. One of the drones detonated over what is described as a large gathering of Venezuelan national guard, reports agree on hundreds soldiers in ranks, but only 7 or 8 were even injured. Shortly after a second drone crashed into nearby apartment building injuring 1. Which has to make it one of the most ineffective drone attacks in modern history.