Terrorist leader Abu Bakr al-Baghdadi, who the president said was killed during a special forces raid in Syria, had reportedly been the captor and rapistof Arizona's Kayla Mueller, who was taken hostage in 2013.

“What this man did to Kayla — he kidnapped her,” her father Carl Mueller, his voice choking, told The Arizona Republic on Sunday morning, shortly after President Donald Trump announced al-Baghdadi had died.

“She was held in many prisons," Carl Mueller said. "She was held in solitary confinement. She was tortured. She was intimidated. She was ultimately raped by al-Baghdadi himself."

"He either killed her or he was complicit in her murder," Carl Mueller said. "I’ll let people who read this article make up their own mind how a parent should feel.”

UPDATE:Here's what Trump's staff told Kayla Mueller's parents about ISIS raid

Carl and Marsha Mueller, from their home in Prescott, said they had mixed emotions.They suspect that had al-Baghdadi been caught alive rather than dead, he would not have been cooperative in sharing information.

“I still want to know, ‘Where is Kayla?’ and what truly happened to her and what aren’t we being told,” Marsha Mueller said. “Someone knows, and I’m praying with all my heart that someone in this world will bring us those answers.”

Mueller grew up in Prescott and went to Northern Arizona University before traveling the world as an aid worker. While working in Turkey, she crossed into northern Syria with a companion to visit a hospital.

Mueller became one of four Americans held hostage by ISIS, including journalist James Foley, who once taught at an elementary school in Phoenix. Like Foley's family, Carl and Marsha Mueller kept their daughter's captivity secret — complying, they said, with the demands they received from her captors and the urging of U.S. authorities who worked on her case.

She was kidnapped and held for 18 months before her death was announced in early 2015. Her parents eventually confirmed her death, but her body has never been recovered.

Family hopes for answers

On Sunday, the Muellers praised President Donald Trump and the soldiers who pulled off the mission.

"We are so grateful for them ... we are so grateful," Marsha Mueller said. They were glad there was no loss of life on our side. They are grateful their daughter and the others who were tortured and killed by ISIS have not been forgotten.

"I still say Kayla should be here, and if Obama had been as decisive as President Trump, maybe she would have been," Marsha Mueller said.

"For me what matters most I'm hoping now we will finally get the answers we have been asking for all along," Marsha Mueller said. "I think this administration truly might help us. I don’t think they are as closed about what happened."

MORE: For Kayla Mueller's family, dark details of the past

Carl Mueller said he was comforted when Trump mentioned his daughter twice in his morning press conference.

"He knows her story. He's been briefed on it, and he knows, and that’s important to me," Carl Mueller said. "I don’t think anything would have stopped him from getting this guy."

After Kayla's death, the Muellers became outspoken critics of the American government's handling of its foreign hostages. They had been encouraged to keep her captivity secret, and discouraged from attempting to free her or pay a ransom.

Carl Mueller also became a vocal supporter of Trump's candidacy for president, speaking at his rallies on the campaign trail.

'A sick and depraved man'

Months after the Muellers confirmed their daughter's death in 2015, U.S. special forces killed ISIS leader Abu Sayyaf and apprehended his wife, known as Umm Sayyaf. Soon, reports emerged that Umm Sayyaf had been responsible for holding Mueller captive so that al-Baghdadi could rape the American repeatedly.

The U.S. Justice Department later issued a criminal complaint against Umm Sayyaf, alleging she conspired to support ISIS and was responsible for Mueller's death, as well as the captivity of others. "The captives were at various times handcuffed, held in locked rooms, and Mueller was sexually abused by Baghdadi," Justice officials charged.

Umm Sayyaf was handed over to the justice system of the Kurdish government in northern Iraq. Then-Sen. John McCain, at the time, questioned the decision not to extradite the woman.

“Sayyaf was clearly involved at the top levels of a foreign terrorist organization with which the United States is in a state of hostilities,” McCain wrote in a letter to the heads of the Pentagon and the Justice Department.

For years, Al-Baghdadi remained one of the most-hunted terrorists in the fight against ISIS. On Sunday, President Trump announced he had died after running from a house into a dead-end tunnel while being chased by United States Special Operations commandos in Northwest Syria.

"He was a sick and depraved man, and now he's gone," Trump said.

But the Muellers know it is not over, and they have faith that President Trump will continue to hunt down others involved. "They’re going to get them all," Carl Mueller said.