The third possibility for Richard - it was done on his behalf, but without his knowledge. I don’t find it at all likely that he killed them himself - why get your hands dirty when there are so many people scrambling for position? Which may bring us to someone taking a proactive step and doing him the favor. The same can be said for Henry, but Henry is still gathering his power base in exile at that time. (And frankly, I think his mother is more likely than Henry - there was an ambitious bitch of a woman).
And thanks for coming back to the wine thing, I was going to look that one up.
I don’t see anyone taking the step of killing the boys without Dicks says so. It just has too many risks, you would piss off a powerful family that still might come to the throne, you could easily find yourself being punished by a King, annoyed that you killed his nephews, you could also be used as a scapegoat and suffer a very unpleasant execution,
Its an era in which with great risk comes great reward - or your head on a pike - many, many stupider things were done in order to get a leg up in court.
Buckingham may have also offed the boys to set up his rebellion. His claim to the throne was as good as Henry’s - at the time they were in cahoots, but in the end only one of them would be king. I’d find him to be a much more likely candidate than Henry - he had better access and the timing is right. But I still think it was Richard.