A refugee from North Korea, who served in the security forces, said (on a British television show) that political prisoners were regularly used as test victims to determine the effect of chemical and biological weapons. North Korea later denounced this, as one would expect, but the South Korean government said that such charges would have to be investigated. The South Koreans have consistently played down atrocities committed by the North Koreans against their own population. This is part of the price of access to the North for Southerners. South Korea believes that eventually they can moderate the brutality of the North Korean government, and get it to reform economically and become something like China. The Chinese have suggested this as well. The problem with this is that China and North Korea have taken very different paths over the last half century. Over two decades ago, China began economic reforms, North Korea only began feeble attempts at reforms in the last two years. China's police state was never as brutal and overwhelming as  the one in North Korea.