– Kayla Mueller’s captivity was different.

The Islamic State in Iraq and the Levant is known for the bloody, fiery and public deaths of its prisoners. The extremists show no mercy, even toward women. They have beheaded journalists and aid workers, tossed suspected gays from tall buildings and tortured children with electric cables.

And yet, whatever private horror Mueller, 26, endured for 18 months, her life as a hostage and her death, possibly in a coalition airstrike, were kept out of the public eye.

That’s no comfort for the family in Arizona mourning a young humanitarian worker who spent her short life helping civilians in conflicts, but it adds one more wrinkle to Western understanding of an extremist group that typically shows zero leniency.

“We don’t know why Kayla was treated differently,” said a source close to her family.

At a news conference Tuesday, Mueller’s family and friends described her as generous and caring, a free spirit who was full of empathy.

“She did ordinary things to extraordinary measures,” said Kathleen Day, a friend.

In a letter to her family in early 2014, Mueller wrote she was in “a safe location completely unharmed + healthy (put on weight in fact); I have been treated w/ the utmost respect + kindness.”

Family members declined to assign responsibility for the looming mystery of Mueller’s ordeal: how she died.

ISIL announced Friday that she had died in a Jordanian airstrike on the building in Syria where she was being held. On Tuesday, the Pentagon acknowledged that Jordanian and American aircrews had struck the target. They refused to connect her death to the strike on what they said was a weapons depot.

U.S. officials didn’t dispute Mueller’s fate, confirming that she was dead after ISIL sent the family unspecified “additional information” that was passed on to government intelligence analysts.

No matter how she died, U.S. officials said, ISIL ultimately bore the guilt. She had been a hostage since she was seized in August 2013 after leaving a Doctors Without Borders hospital in Aleppo, Syria.

The confirmation of Mueller’s death raised the question of whether the United States ought to reconsider its policy of refusing to negotiate ransom payments for citizens taken hostage. Mueller was the fourth American to die in ISIL custody in the past seven months. Three were beheaded — even as a dozen or so Europeans were released after money exchanged hands.

A person with knowledge of Mueller’s case said the captors had demanded a multimillion-dollar ransom and floated the idea of a prisoner swap for Aafia Siddiqui, an accused Al-Qaida operative who was convicted of trying to kill Americans.

President Obama was adamant that the U.S. would not change its policy. “Once we start doing that, not only are we financing their slaughter of innocent people and strengthening their organization, but we’re actually making Americans even greater targets,” he told BuzzFeed.