There is no need to produce evidence for something that you are not asserting.

Keeping an open mind is not the same as making an accusation.   It's no more rational to rule out the accusation made by the acting President of Venezuela than it would be to assume that it is justified.   Inevitably we make estimates of what feels more likely to us
- mine would be that Chavez died of natural causes - but these are just subjective guesses, and we shouldn't treat them as certainty.