This month, ISIS perpetrated the worst terrorist attack in modern Turkey’s history. Today, it dispatched an assassin to murder two Syrian activists from the “capital” of the so-called caliphate, and wasted no time boasting of its cross-border reach.

Fares Hammadi and Ibrahim Abd al-Qader were both members of the grassroots anti-ISIS monitor organization known as Raqqa is Being Slaughtered Silently (RBSS), which this year won the Committee to Protect Journalists’ International Press Freedom Award. Not long after the jihadist takeover of their hometown of Raqqa City in 2014, they fled to Urfa, southern Turkey, where they set up shop coordinating the group’s media from a putatively safe place. But ISIS found them somehow.

“In the morning, somebody, we don’t know who, exactly, but he was from ISIS—entered their apartment and shot them in the head,” Abu Ibrahim al-Raqqawi, one of the Raqqa-based members of RBSS, told The Daily Beast via Skype. “Then he beheaded them. There was a third friend who was coming to the apartment. He found their bodies. He was shocked.”

Nothing was confiscated from Ibrahim and Fares’s apartment. Their computers and equipment were untouched. “He just killed them and left.”

“They were very brave people,” al-Raqqawi added. “The bravest people I ever met. They were filming in the very sensitive places, filming ISIS in battle, covering the barrel bombs. Every time there was an airstrike in the city, they were the first guys to go and film.”

ISIS has claimed responsibility; it’s also celebrating on social media. An ISIS media account on Twitter published a screenshot from a cellphone showing Ibrahim and Fares posing together in an old photograph (they’d posted it themselves when it was taken). The sick, mocking caption reads: “A selfie before being slaughtered silently.”

Ibrahim and Fares aren’t the only ISIS victims from RBSS. In July, the jihadists shot at point blank range in the head Bashir Abduladhim al-Saado and Faisal Hussain al-Habib. Then, less than a month ago, they did the same to Rakan Awad and Atallah al-Khalaf, and Mohammed al-Mousa, the father of Hamad al-Mousa, an RBSS activist ISIS has not caught.

“We are a lot,” al-Raqqawi said. “We will not stop. It’s our city. We will defeat them.”