Kayla Mueller wanted to help. Instead, the aid worker was captured by ISIS. Today her family and the White House confirmed her death, days after the militant organization said she died in an airstrike. Her parents didn’t offer details, but they did release a letter she wrote. Her case is already prompting questions about policies barring negotiations with terrorists, especially as the parents of another American captive say U.S. officials threatened criminal charges if the family paid an ISIS ransom.