Apparently Pope Francis also played a key role in the negotiations and was the only other foreign leader directly involved in some of the talks. In particular, he took on the cause to have Alan Gross released and also sent personal letters to both leaders urging them to make peace.
http://www.washingtonpost.com/blogs/...ee-alan-gross/
http://www.usatoday.com/story/news/w...deal/20533525/
http://www.buzzfeed.com/evanmcsan/wh...al#.elQ7zOmkDY