As Kurdish forces open routes back to the northern Yazidi city of Sinjar, Iraq, fighting back armies of Islamic State jihadists, the Yazidis returning home are increasingly turning on their Arab former neighbors, rage increasing with each new discovery of a mass grave.

In an extensive report by Reuters, a number of former residents of Sinjar report that, in the time the Islamic State controlled the area, hundreds — if not thousands — of the tiny religious minority were killed and shoved into mass graves in what is almost universally regarded as an attempt to commit genocide. In response to the siege, which lasted from August until very recently, some Yazidis are taking up arms against the Arab Muslims whom they believe collaborated with Islamic State to rape, enslave, and slaughter other Yazidis.

Reuters spoke with “more than a dozen Sunni Arab residents,” who reported revenge killings, looting, mass theft, and other forms of violence from returning Yazidis. At least 21 Sunni Arabs have been killed since the Kurdish forces expelled the majority of the Islamic State fighters in the area, while 17 are missing.

In one town in the Sinjar area, Arab witnesses reported that “dozens of civilian cars began to arrive from the direction of Gohbal and men, whom the Arab villagers identified as local Yazidis helped themselves to household appliances, vehicles and livestock.” Women claimed their jewelry was stolen off their bodies while personal belongings were also looted. The village of Sibaya, claim the Arab witnesses, was set on fire in retribution.

The attacks Reuters reports of are eerily reminiscent of Yazidi testimony of what they endured when the Islamic State temporarily overtook the area. “It wasn’t even IS who did most of the killing,” one Yazidi witness said of the Sinjar siege in August, “it was our Sunni Arab neighbors… We looked after these people’s children, and as soon as ISIS appeared, they immediately turned against us.” At the time, many Yazidi survivors interviewed by major media outlets vowed never to return to Sinjar.

The Islamic State sieged the area in August, sending the Yazidi population of Sinjar fleeing in all directions. Some escaped towards the Kurdish stronghold of Erbil. The less fortunate climbed up Mount Sinjar, where thousands were stranded without food or water, and many died of starvation and heat waiting to be saved.

Even today, the Islamic State has not been eradicated from the area. “The peshmerga and the Yazidi volunteers did get inside the city of Sinjar,” said Murad Ismael, a worker with the Sinjar Crisis Group, “About three-quarters of the city has been recaptured. However, there are still ISIL snipers. ISIL have been cleared from the northern side of the mountain, but they left behind IEDs [improvised explosive devices]. The southern side of the mountain is not safe.” Ismael told Al Jazeera that Kurdish forces returning to Sinjar also found a number of abandoned Arab villages that appeared to have been targeted by airstrikes.

The reprisal attacks are highlighting a problematic rift among the Kurds, of which the Yazidis are a religious minority. Reuters notes that a prominent Yazidi fighter working with the Kurdish Democratic Party (KDP), led by Iraqi Kurdish President Masoud Barzani, was frequently mentioned as leading the attack on local Arabs. When questioned, however, he appeared to blame the Kurdistan Workers’ Party (PKK), a Marxist group still designated as a terrorist group by the United States. The PKK, which operates largely in Turkey, denied involvement.

As Al Monitor notes, tensions between the PKK and the KDP have been simmering under the greater struggle against the Islamic State for months. The Peshmerga’s inability to prevent the siege of Sinjar has caused local Yazidis to question their faith in Barzani, particularly since he is of Kurdish Muslim — not Kurdish Yazidi — background. “Barzani now wants to return as the liberator of Mount Sinjar, but he has no intention of sharing the glory with the rising star of the region, the Kurdistan Workers Party (PKK),” notes Al Monitor, “Barzani also does not want Yazidi self-defense forces under control of the PKK to be an alternative to his peshmerga forces.

If Reuters’ reports are accurate, at least some of the Yazidi Peshmerga may be doing just that: rallying civilians into a Yazidi self-defense force, ensuring that recent history does not repeat itself.