Obama Confirms U.S. Hostage Kayla Mueller Killed by ISIS

U.S. President Barack Obama on Tuesday confirmed the death of Kayla Mueller, a U.S. aid worker who had been held hostage by Islamic State militants, saying the United States would "find and bring to justice the terrorists who are responsible."

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Mueller's family also said in a statement that they were "heartbroken" to learn of her death and released a copy of a letter she had written in 2014 while in captivity.

U.S. aid worker and hostage Kayla Mueller was determined to have died after her Islamic State captors reached out privately to her family over the weekend, a White House spokeswoman said on Tuesday.

"Over the weekend, the family received a private message from Kayla's ISIL captors containing additional information," spokeswoman Bernadette Meehan said, using an acronym for Islamic State.

"Once this information was authenticated by the intelligence community, they concluded that Kayla was deceased."

Last week, Mueller's parents expressed hope that their daughter was still alive, despite ISIS' claim that she had been killed by a Jordanian airstrike in Syria.