The White House is confirming that 26-year-old Kayla Jean Mueller is the fourth American hostage to be killed by ISIS. Mueller, who was a humanitarian aid worker helping Syrian refugees, was captured by the terrorist group in 2013.

Several days ago ISIS stated that Mueller had been killed by a Jordanian airstrike, which Jordan denied. The country's foreign minister also took to Twitter to air its suspicions that ISIS was telling the truth.

The White House also expressed doubt that Mueller’s death was caused specifically by an airstrike, but then on Tuesday (Feb. 10) the Obama administration confirmed Mueller’s death.

“Over the weekend, the family received a private message from Kayla’s ISIL [ISIS] captors containing additional information,” explained Bernadette Meehan on behalf of the National Security Council. “Once this information was authenticated by the intelligence community, they concluded that Kayla was deceased.”

"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," President Obama said.

Mueller is a new name added to a list of journalists and aid workers from America, the UK and Japan who have been taken hostage then killed by ISIS. The White House and Mueller’s family both stressed Mueller’s selflessness and her desire to help others, wanting that part of her to be remembered most.

“Kayla dedicated her life to helping others in need at home and around the world,” The White House said. “In Prescott, Arizona, she volunteered at a women’s shelter and worked at an HIV/AIDS clinic. She worked with humanitarian organizations in India, Israel, and the Palestinian territories, compelled by her desire to serve others."

Her path eventually led to Turkey, where Mueller helped provide comfort and support to Syrian refugees forced to flee their homes during the war. "Kayla’s compassion and dedication to assisting those in need shows us that even amongst unconscionable evil, the essential decency of humanity can live on.”

Mueller’s family wanted us to not only remember her, but the people she was helping who still need help. “We are so proud of the person Kayla was and the work that she did while she was here with us,” her family said in a statement.

“She lived with purpose, and we will work every day to honor her legacy. Our hearts are breaking for our only daughter, but we will continue on in peace, dignity, and love for her. We remain heartbroken, also, for the families of the other captives who did not make it home safely and who remain in our thoughts and prayers. We pray for a peaceful resolution of the conflict in Syria.”