3 guys 1 hammer is a video of some kids killing a guy, but there's no plot so I don't think it counts as a "snuff film," and by "homemade snuff films" do you mean they have a plot and some production value, lighting, scripting, and someone dies, or do you mean "murder that was filmed?" Because that's kinda my point I don't know if it counts without a plot.

gruesome one of a prison riot in south america,

See from this description I don't count that as a "snuff film," and I'm questioning if it counts, because of course "filmed death" isn't a myth, there's countless examples. A quick search defines "snuff films" as:

snuff film

noun

A movie in a purported genre of movies in which an actor is actually murdered or commits suicide

A film that shows, or purports to show, the actual deliberate killing of one of the performers.

So that seems to suggest that I'm right.