Newly discovered documents have revealed that the Islamic State kept records of the number of slaves owned by each of its fighters.
The documents obtained by the Washington Post list each militant's name, country of origin, country of residence, date of birth, blood type, and weapons specialties. Additionally, the forms also include a section listing the fighters' number of wives and children, as well as the number of slaves each one owned.
The papers also suggested that many of the terror group's foreign recruits are now refusing to join the battle in Iraq, and some are trying to flee the region.
The documents, containing details of 14 "problem" fighters from the Tariq Bin Ziyad battalion, were found by Iraqi forces after they captured an ISIS base in a neighborhood in Mosul last month.
In November, Iraqi forces discovered documents, posters, and other printed materials highlighting the terror group's rules regarding slaves, beard length, and giving of alms.
One leaflet stated that senior ISIS clerics are responsible for distributing female captives to its fighters. Non-Muslim women can be taken as concubines, and militants are allowed to own two sisters, but they can only have sex with one. It also indicated that the militants are not allowed to share a concubine.
"Pre-pubescent girls can be taken as concubines. You cannot have penetrative sex but you can still enjoy them," read the leaflet.
A former ISIS captive has revealed that ISIS has abused over 6,500 women and girls as young as nine.
Nadia Murad, a Yazidi woman who was captured by the extremists when she was 19 in August 2014, said that she was raped by 12 different men.
"They separated any woman over nine years old and were enslaving them they forced us to change our religion and they did everything they wanted to us," Murad recounted. "We were subjected to crimes to their hands that nobody can mention what they did for us," she added.
She said that her sister was also captured along with her, but ISIS executed their mother because she was considered "too old."
Murad was able to escape from captivity after three months, and she has since fled to Germany. She has been traveling around the world to raise awareness about the plight of Yazidi women captured by ISIS.