Colleagues and family say Kayla Mueller was dedicated, bright and compassionate. The 26-year-old humanitarian aid worker died recently in the custody of Islamic State militants, though details of how, where and when she died remain unclear.
FILE - This undated handout photo shows 26-year-old Kayla Mueller(L) and her mother Marsha Mueller.
A native of the southwest U.S. state of Arizona, Kayla Mueller graduated from Northern Arizona University in 2009 and headed abroad. She improved her language skills working as a nanny in France, then traveled to India and the Middle East as a humanitarian aid worker.
Mueller's former professor, Carol B. Thompson, told local media the woman and her family knew the career could be dangerous.
"She knew exactly what she was doing. She was not the itinerant tourist. She was the highly committed peacemaker," Thompson said.
By 2012, she was working with refugees on Syria's border with Turkey while an uprising against Syrian President Bashar al-Assad became increasingly violent and displaced hundreds of thousands of people.
"Syrians are dying by the thousands, and they're fighting just to talk about the rights we have," Mueller told an Arizona newspaper on a trip home in early 2013. "For as long as I live, I will not let this suffering be normal.”
Mueller was kidnapped in August that year as she left a hospital run by the Spanish branch of Doctors without Borders in Aleppo.
In a letter dated 2014, the aid worker told her family she was safe and being treated well.
"None of us could have known it would be this long, but know I am also fighting from my side in the ways I am able [and] I have a lot of fight left inside of me," Mueller wrote. "I am not breaking down [and] I will not give in, no matter how long it takes."
Her family, in a statement released Tuesday following confirmation of her death, said: "We are so proud of the person Kayla was and the work that she did while she was here with us. She lived with purpose, and we will work every day to honor her legacy."