Major General Yoav Mordechai, the Coordinator of Government Activities in the Territories, told US Special Envoy Jason Greenblatt that Israel refuses to allow Gaza to be developed while Hamas holds on to Israeli MIA's. Hamas has the bodies of IDF soldiers Hadar Goldin and Oron Shaul, who were both killed in 2014's Operation Protective Edge.
Hamas is also holding Israeli Avraham Mengistu in its custody.