When a notorious Russian assassin and an American newspaper correspondent boarded separate planes in Turkey on Thursday, it marked the culmination of a secretive, dramatic prisoner swap deal between Russia and the West that was years in the making.

The origins of this deal, which involved two dozen prisoners, can be traced back to 2022. But behind-the-scenes negotiations between Russia, the US and four European countries ramped up earlier this year before intensifying in recent weeks as a final agreement came into view for all sides.

Those negotiations were at times feverish and testing. They also came as US-Russia tensions soared over the Ukraine war. "It was the culmination of many rounds of complex, painstaking negotiations over many, many months," Jake Sullivan, the US national security adviser who played a critical role in the deal, said shortly after the exchange.