The parents of Kayla Mueller, the 26-year-old American who was kidnapped by the Islamic State and killed in 2015, said Wednesday that the decision to name the ambitious operation that killed Islamic State leader Abu Bakr al-Baghdadi in their daughter’s honor was “an amazing gift."

Mueller, who was described by her family as a “devoted humanitarian,” traveled to Turkey in 2012 and crossed the border into Syria, on a mission to help those fleeing the civil war in the country. She was leaving a hospital run by the medical charity Doctors Without Borders in the Syrian city of Aleppo when she was kidnapped in August 2013.

Talking to “Today” on NBC News on Wednesday, Mueller’s parents, Carl and Marsha Mueller, opened up about their loss and acknowledged that it was hard to express how they felt at the news of Baghdadi’s death.

“I’m glad that evil person is gone,” Mueller’s father said. “If you were a parent and this man did what he did to Kayla, to your child, and then they got him, how would you feel?”

Mueller’s mother said of the mission being named after their daughter: “That was just an amazing gift for Kayla,” she said. “I know Kayla; Kayla would say this was for all of us. This is for all the hostages.”

In 2016, federal prosecutors offered more details about the abuse that Mueller is said to have suffered in captivity when they charged an Iraqi woman with playing a role in Mueller’s imprisonment. Nisreen Assad Ibrahim Bahar told FBI agents that Mueller and other captives were kept in locked rooms and sometimes handcuffed. The affidavit indicates that Mueller was made to watch disturbing Islamic State propaganda videos and was raped by Baghdadi.

In February 2015, ISIS claimed that Mueller was killed when a Jordanian fighter plane bombed the building in which she was being held. U.S. officials expressed skepticism about the claim, while the Jordanian government denied its airstrikes had killed the U.S. hostage.

The precise details surrounding Mueller’s death and the whereabouts of her body are unclear, with her parents saying Wednesday that they had a slight hope that she still might be alive.

In remarks Sunday, President Trump described in detail the operation that killed Baghdadi, saying that he “died like a dog” and that he blew himself up in a “dead-end tunnel” as U.S. troops moved in on him and three of his children.

Speaking to NBC News on Sunday, national security adviser Robert C. O’Brien described Baghdadi as a “brutal, vicious terrorist” and said that the United States had finally brought to justice a man with a history of killing Americans, including journalists James Foley and Steven Sotloff.

Calling Mueller a “great young American,” O’Brien said it was Gen. Mark A. Milley, chairman of the Joint Chiefs of Staff, who decided to name the operation that killed Baghdadi after her.

Speaking to the Arizona Republic on Sunday, Mueller’s parents praised Trump’s handling of the raid and expressed hope that they would one day find out more about what happened to their daughter.

“I still want to know, ‘Where is Kayla?’ and what truly happened to her, and what aren’t we being told?” Mueller’s mother, Marsha, told the newspaper.

“I still say Kayla should be here, and if Obama had been as decisive as President Trump, maybe she would have been,” she added. The Muellers have been critical of the Obama administration in the past, telling ABC News in 2016 that it took more than 17 months for President Barack Obama to follow up on his promise to donate money to the Kayla’s Hands foundation.

“The president could have been a hero, but he chose not to be,” Mueller’s father, Carl, told ABC News.

Describing his daughter’s ordeal at the hands of the Islamic State, Mueller’s father said: “She was held in many prisons. She was held in solitary confinement. She was tortured. She was intimidated. She was ultimately raped by al-Baghdadi himself."

While in captivity, Mueller penned a letter to her family urging them not to let her situation burden them. “I DO NOT want the negotiations for my release to be your duty,” she wrote, adding: “I know you would want me to remain strong. That is exactly what I am doing.

“I remember mom always telling me that all in all in the end the only one you really have is God. I have come to a place in experience where, in every sense of the word, I have surrendered myself to our creator,” she wrote, invoking her religious beliefs throughout the letter.