Story highlights Ouruba Barakat was a longtime activist with the Syrian opposition

Daughter Halla was an American journalist working for Orient TV

Istanbul (CNN) Mourners gathered at a mosque in Istanbul on Saturday to pay their respects to a Syrian activist mother and her American journalist daughter who were found slain in their home on Thursday.

Their coffins were laid out on marble slabs in front of the mosque and draped in the three-star Syrian revolution flag -- a tribute to Ouruba Barakat and her daughter Halla's commitment to the uprising in Syria. Their prayer services were held at Fatih Mosque as crying friends and family looked on.

Some funeral attendees flew flags with "Free Syria" written on them.

The Istanbul killing was uncovered when friends began to worry that 22-year-old Halla was not responding to phone calls and text messages. They notified authorities, who discovered the stabbed bodies in their home located on the Asian side of the Bosphorus River.

They had been wrapped in a blanket with detergent poured over it, state news agency Anadolu reported. Authorities suspect the detergent was used to cover up the smell, according to Anadolu. There was no sign of forced entry in the preliminary investigation, the news agency said.

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