Iraqi authorities have commenced the excavation of what is believed to be a mass grave left by the Islamic State extremist organization during its violent campaign throughout the country a decade ago.

Local authorities are collaborating with the courts, forensic experts, Iraq’s Martyrs’ Foundation, and the mass graves directorate to conduct the excavation at a sinkhole site in al-Khafsa, situated south of the northern city of Mosul, as reported by the state-run Iraqi News Agency on Sunday.

Ahmad Qusay al-Asady, who heads the mass graves excavation department at the Martyrs Foundation, informed The Associated Press that his team started their work at Khasfa on August 9 after being requested by Nineveh province’s Governor, Abdulqadir al-Dakhil. The primary aim of this operation is to gather visible human remains and surface evidence while preparing for a complete exhumation that officials believe will require assistance from international experts.

After the initial 15 days of work, the foundation’s teams in Mosul will establish a database and begin collecting DNA samples from families of the presumed victims. Al-Asady stressed that lab processing and creating a DNA database should be the main focus to ensure accurate identification. Full exhumations can only take place once specialized help is available to manage the hazards at the site, such as sulfur water and unexploded bombs. Khasfa is described as “a very complicated site,”

According to unverified reports from witnesses, families, and other unofficial sources, authorities suspect that thousands of bodies could be buried there, he said.

Many mass graves containing thousands of bodies, thought to be victims of the extremist group, have been found in Iraq and Syria.

At its peak, IS controlled an area about the size of half the United Kingdom in Iraq and Syria, becoming notorious for its brutal violence. They killed civilians and forced many Yazidi women, one of Iraq’s oldest religious groups, into slavery and sexual abuse.

The group’s defeat in Iraq happened in July 2017, when Iraqi forces took over the northern city of Mosul. Just three months later, Kurdish forces struck a major blow by seizing the northern Syrian city of Raqqa, which was the group’s main capital. The fight against IS officially ended in March 2019, when U.S.-backed and Kurdish-led Syrian Democratic Forces took the eastern Syrian town of Baghouz, marking the last area are been controlled by the terrorist.

Rabah Nouri Attiyah, a lawyer who has dealt with over 70 cases of missing people in Nineveh, told the AP that the info he collected from the foundation and various Iraqi courts during his investigations indicates that Khasfa is “the biggest mass grave in modern Iraqi history.”

However, Al-Asady mentioned that investigators “can’t confirm yet if it’s the largest mass grave” found in Iraq, “but given the size of the area, we think it’s one of the largest.”

Attiyah pointed out that around 70% of the human remains discovered at Khasfa are believed to belong to Iraqi army and police personnel, with other victims including Yazidis. He shared that he has talked to many eyewitnesses from the area who saw IS fighters taking people there by bus and executing them. “A lot of them were decapitated,” he noted.

Attiyah’s uncle and cousin were police officers killed by IS, and he is among those who are keen to identify and recover the remains of their loved ones.

Testimonies and witness accounts, along with evidence from other mass graves in Nineveh, suggest that most military, police, and other security forces personnel killed by IS are likely to be found at Khasfa, along with Yazidis from Sinjar and Shiite victims from Tal Afar, he added.