The proverb 死人【しにん】に 口【くち】 無し【なし】 (the dead do not have a mouth) is listed e.g. here and I've also heard it from my (native) teacher.
Here's what I'm wondering:
From what I've heard so far, it should be understood to mean "You can say anything about a dead person. They will not talk back". Is that how everyone will understand it? I want to be sure that I'm using it correctly. An alternative interpretation would be "If you want someone to keep her mouth shut, kill her". Can I be sure that this is never meant? (I could imagine such a thing being said in a gangster movie)
How old is this saying/are its origins known? Is it connected to a religion, is it maybe originally Chinese, etc.?