President Obama confirmed on Tuesday that Kayla Mueller, 26, an American hostage held by ISIS, has indeed been killed. As new details emerge about her experience in captivity, some officials are believing that she may have been given over to a jihadi commander. A counter-terrorism official told ABC News that ISIS did not see her as either a bargaining chip or a hostage.

The limited collection of intelligence available indicating that Mueller was still alive included indirect information such as ISIS referring to her in calls, or fighters seen guarding a site where she may have been held. The evidence indicated that sometimes she was in the company of an ISIS leader who was being actively tracked, and other times she was not. The leader may have had custody of Mueller, possibly through forced marriage.

The Mueller family said that in private communications the terrorists had referred to her as a guest. In a letter Kayla wrote to her family last year, which was released by the family on Tuesday, she said she was unharmed, healthy and in a safe location.

Former head of the National Counterterrorism Center Matt Olsen said that ISIS is known for “essentially selling off” young women and girls to ISIS militants. However, several counter-terrorism officials said that they had a few ideas but no solid information of where she has been in Syria over the past months. A few weeks ago U.S. officials lost track of her entirely, and the Mueller family had received no proof of life such as an audio recording of her voice since last May.

The confirmation of Mueller’s death comes a few days after the terrorist group claimed that she died as a result of a Jordanian airstrike that was launched last week in retaliation for ISIS burning one of their captured pilots alive. Although last Friday ISIS claimed that she had been killed, no proof was presented and there were doubts about the claim. A White House National Security Council spokesperson said today that the Mueller family received an email and a photograph from the captors over the weekend that contained additional information. The information was authenticated by American intelligence, who concluded that aid worker was dead.

At this time it is unclear how or when Mueller was killed. An intelligence official said that there was no evidence that her death was the result of an airstrike, as ISIS claimed. Although she was thought to be the last American held hostage by ISIS, White House spokesperson Josh Earnest said on Tuesday that they are aware of other Americans being held hostage in the region.