Well the person does not have to be in the US merely in a country that has an extradition treaty, is willing to extradite for a price in the game of geopolitics, or the US thinks it can perform a rendition.

In any way it is also a signal to the world. Do t forget about Ukraine and the Russians are doing terrible things there.

It probably also helps pressure the GOP to put forward a vote for aid to Ukraine. If they don't they don't care about Russians torturing Americans. And that's not an easy thing to spin for the GOP spindoctors.