President Barack Obama said that Mueller, who worked with Syrian refugees, “epitomised all that is good in our world.”
“No matter how long it takes, the United States will find and bring to justice the terrorists who are responsible for Kayla’s captivity and death,” the president said.
Mueller was the only known remaining US hostage held by the Islamic State group. She was taken into captivity in August 2013 while leaving a hospital in Syria.
US vice-president Joe Biden also paid tribute to the young aid worker, calling her “a compassionate young American who represented everything good about the human spirit”.
“There are no words to express to Kayla’s parents, Marsha and Carl, how sorry we are for their crushing loss, just how much so many wished for and worked to try and secure a better outcome, or how awe-inspiring is the example of their strength, determination, and devotion to faith and family,” he continued. “To them, and to Kayla’s brother Eric and his family, I hope they can know that our entire country grieves together with all those whose lives she touched.”
Mueller had “one mission in life from the very start, and that was to help people,” Biden said. She worked on aid projects in India, Israel, and the Palestinian Territories, with people at an HIV/AIDS clinic and a women’s shelter at home in Arizona, and, most recently, Syrian refugees in Turkey.
She was active in campaigning for Darfur during her university years, writing letters, lobbying members of Congress, and conducting two silent walks. Her high school teacher told a local paper at the time that he could envision a then 19-year-old Mueller “running an activism group, or getting involved in national or international politics.”
She worked in Turkey and Syria with the international humanitarian aid agency Support to Life. In an article published in her local paper The Daily Courier before she was kidnapped, Mueller pleaded for aid for those she was helping.
“Syrians are dying by the thousands, and they’re fighting just to talk about the rights we have,” Mueller said. “For as long as I live, I will not let this suffering be normal, something we just accept. It’s important to stop and realise what we have, why we have it and how privileged we are. And from that place, start caring and get a lot done.”