American Held by Islamic State, Is Confirmed

President Obama Vows to Bring Justice to Those Responsible for Death.

Kayla Jean Mueller, the last American hostage known to be held by Islamic State extremists, was confirmed dead by her relatives and the White House on Tuesday.

Ms. Mueller’s parents received what U.S. officials described as private communications from Islamic State over the weekend, including photographs. Based on the images, U.S. intelligence agencies concluded they proved she had been killed, officials said.

However, intelligence officials couldn’t determine how she was killed or when she died, White House press secretary Josh Earnest said.

The extremist organization asserted Friday that Ms. Mueller had been killed in a Jordanian airstrike in Syria. But U.S. and Jordanian officials have been skeptical of the claim. U.S. officials said it was impossible to ascertain from the photos whether she had been killed in the recent strikes as the group claimed.

“We are so proud of the person Kayla was and the work that she did while she was here with us,” Ms. Mueller’s family said, calling her “a compassionate and devoted” humanitarian. “She lived with purpose, and we will work every day to honor her legacy.”

She had been held by Islamic State for 18 months, describing her captivity in a letter that she wrote last spring and that was released by her family Tuesday.

Unlike the experiences of other Islamic State hostages, she said in the letter that she hadn’t been physically harmed.

During Ms. Mueller’s captivity, U.S. intelligence officials had assessed that Islamic State militants didn’t intend to kill her, and believed that she wasn’t in the same mortal danger as the male hostages have been.

“She was not at the same risk,” said a military official. “They have treated their female hostages differently.”

U.S. officials also believe Ms. Mueller was forced to convert to Islam and marry an Islamic State leader, part of the reason why they assessed she wouldn’t be killed.

Ms. Mueller, who was 26 years old, traveled to the Turkey-Syria border region in December 2012 to work with aid organizations Support to Life and the Danish Refugee Council, according to relatives, to help refugees displaced by the Syrian civil war. She was kidnapped in Aleppo in August 2013.

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