The answer in this scenario is the same as before: if the extraditing country, aware that this is a possibility, allows the extradition to go ahead, then the pe

The answer in this scenario is the same as before: if the extraditing country, aware that this is a possibility, allows the extradition to go ahead, then the person extradited has been subject to due process in their country. In addition, the victims of Y and Z may reasonably consider it unfair if the perpetrator avoids prosecution on this basis. If Y and Z were a crime in in the perpetrator's country, it would not be unfair for him to be prosecuted for them, even if the evidence, or his being in custody, came only from his being arrested for X; this happens quite frequently. It also sometimes happens that extradition is made conditional - for example, on the condition that the person is not subject to the death penalty. For a couple of obvious reasons, reneging on such an agreement after the extradition would have negative long-term consequences for the country that does it.