Transcript for Syrian-American journalist and her mother killed in Turkey

We're back now with the double murder mystery. This story involves an American born journalist and her mom. They appeared on ABC last year because they were friends with Kayla Mueller, the young aid worker who was kidnapped wby ISIS and killed. Reporter: She was only 23 but the human rights work of american-born journalist Halla Barakat and her activist mother orouba Barakat made for a powerful team and also put them at great risk. I met them last year in Turkey for an ABC news report on the young American hostage, Kayla Mueller, who they had befriended shortly before she died in ISIS captivity, a death they felt deeply. We're two women that we know it's a cruel world out there for women. Reporter: This week hala and her mother were the victims, found murdered, stabbed and strangled in their istanbul apartment. Friends say they had recently been threatened because of their very public criticism of the Assad regime in Syria. As a reporter for orient TV in istanbul, an anti-syrian regime outlet, the young women had been investigating the horrors of the Assad government. Despite the crises being the worst and most extreme of its kind, international efforts have failed to hear Syria's warning. Reporter: Last year hala talked about her American roots. She was born in North Carolina. And how heartbroken she had been over the death of Kayla Mueller, the American who had come to the region to help the Syrian refugees fleeing war. I'm very American. I'm very Syrian at the same time. So we fit together very easily. She's so young to have this experience to happen. To be dead at this time, at this age. Reporter: Kayla Mueller's parents told ABC news we are numb and do not understand how anyone could do this to our gracious and beautiful friends. The funeral for Halla and orouba Barakat will be held today in istanbul. Because Halla was an American citizen, the FBI says it will investigate. Brian Ross, ABC news, New York. Such a tragedy. Our thanks to Brian Ross for

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