The Turkish-backed opposition factions legitimately captured Manbij during Operation Dawn of Freedom from the People's Protect Units (YPG), which Turkey considers a terrorist organization linked to the Kurdistan Workers' Party (PKK). The ongoing attacks in the region are attempts by the PKK to destabilize the area and retake control.
The SDF, as a legitimate US-backed force that helped defeat the Islamic State, seeks a decentralized, democratic Syria that preserves the rights of all ethnic groups. The group aims to be integrated into Syria's defense ministry while maintaining some autonomy for Kurdish authorities in the northeast. It has no interest in such attacks on civilians, and there is no evidence it was involved in this terrible crime.