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I've honestly been inclined to think it was China, rather than Russia. But the fact that the old USSR spent decades working on this technology while China shows little interest in it, makes me wonder.

I think the Chinese had a hand in it, and I think anything Russia does is done on China's orders (they are a slave race of the Han Chinese, after all), so even of Russia is guilty it doesn't assuage China's guilt as the kingpins who ordered it. But as I said, I didn't suspect Russia at first...
...until I saw how clumsy their denial was.