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The killing of the young Syrian activist took place close enough to his home in southern Turkey that his youngest brother heard his piercing scream.

Ibrahim Abdelqader's attackers stabbed him dozens of times and left his partially decapitated corpse hanging from a doorframe. 

His family and colleagues say he was killed by a secret operative from the Islamic State group who befriended him before the attack. The message from IS was clear: Its enemies are not safe, even across borders.  

More than a month after the murder of Abdelqader and his friend Fares Hamadi, the media collective that Abdelqader belonged to — which secretly documents life at the heart of the Islamic State group's self-proclaimed caliphate — has been forced into deep hiding.  

IS claimed responsibility for the killings in a video message warning that "every apostate will be slaughtered silently."

It was a grim twist on the media collective's name  [RBSS] a reference to the Syrian city of Raqqa that has become synonymous with IS and its efforts to build a caliphate.  

RBSS was honoured last month by CPJ with the  for their 'courageous reporting'.  

Their from Raqqa have tackled everything from the conscription of children to the sexual slavery of Yazidi women brought from Iraq. They have documented public killings, flagged the deaths of Western hostages, and tracked the bombs dropped by the Syrian regime as well as the US, France and Russia.  

Now the Oct. 29 slaying of Abdelqader and Hamadi raises concerns about the safety of anti-IS activists in Turkey, a country that only recently grasped the scale of the terror threat within its own borders.  

The killings extended the reach of the campaign already being waged by IS against the collective.

In the mosques of Raqqa, Friday sermons regularly feature diatribes against the activists. IS killed three men this year that it accused of belonging to the network, although members say they actually were the father and friends of activists.

On Wednesday, Ahmad Mohamed al-Mossa, a Syrian journalist and member of the media collective was murdered by unknown masked men in Idlib, according to the group who announced his death via on Thursday.

Al-Mossa is RBSS's third known journalist killed in Syria for reporting on atrocities committed by Islamic State group in Raqqa city since it was founded in April 2015.