Actually I chose the example of Russia and the Czar for the reason the two were autocrats the country got rid of because they disapproved of their actions. As to why they don't want to go along with the claim of genocide, I suspect there are two reasons. One is that there may very well be an element of truth in their explanation. The other is a lawyerly thing: admitting would open them up to penalties which they would not want to pay since the actions were not under their control. Why pay for someone else's crime?
Guatemala judge orders detention of president in corruption scandal (Reuters)