Behind the deal: Spies, a killer, secret messages and unseen diplomacy

A turning point came June 25, when a group of CIA officers sat across from their Russian counterparts during a secret meeting in a Middle Eastern capital.

The Americans floated a proposal: an exchange of two dozen prisoners sitting in jails in Russia, the United States and scattered across Europe, a far bigger and more complex deal than either side had previously contemplated but one that would give both Moscow and Western nations more reasons to say yes.

Quiet negotiations between the United States and Russia over a possible prisoner swap had dragged on for more than a year. They were punctuated by only occasional glimpses of hope for the families of the American prisoners - including Evan Gershkovich, a reporter for The Wall Street Journal, and Paul Whelan, an American security contractor - growing increasingly impatient for their ordeal to end. Those hopes were...