In cases like there were actually investigating can land the people doing the investigating in prison, I think proceed according to the cautionary principle.

So, if a tyrannical dictatorship like China is accused of abusing human rights and said tyrannical dictatorship is not willing to let people investigate the claims, we can accept the accusations as true until aforementioned tyrannical dictatorship is willing to let people investigate.

No need for 'in dubio pro reo' in such cases.