(Washington Post) Leah Goldin and Simha Goldin - Five years ago this month, our son Hadar Goldin, a second lieutenant in the Israel Defense Forces, was abducted by Hamas militants during a UN-sponsored humanitarian cease-fire in the 50-day war along the Gaza border with Israel. The militants dragged him into the tunnel from which they had apparently emerged. Hadar was killed during the ensuing firefight as Israeli forces raced to try to rescue him. To this day, we believe that Hamas holds our son's remains, presumably as a bargaining chip to extract political concessions - just as it holds the remains of Oron Shaul, another Israeli soldier who was killed during the conflict, as well as hostages Avera Mengistu and Hisham al-Sayed. The UN and U.S. condemned the abduction at the time, but since then have done nothing to press Hamas to return Hadar's remains or those of the others it holds. Meanwhile, international funding and aid flows into Gaza, including from the UN. Even modest pressure from the UN to make some of its aid contingent on Hamas' return of the remains it holds might lead to a solution. On June 11, the UN Security Council passed Resolution 2474 on people reported missing in armed conflict. The resolution insists that combatant groups are obliged to return remains. What's needed now is concrete action by the UN and the U.S. to put these ideas into practice. Leah Goldin is a senior lecturer at Afeka College in Tel Aviv. Simha Goldin is the director of the Goldstein-Goren Diaspora Research Center at Tel Aviv University.