UNITAD, the UN body set up to investigate IS crimes in the country, began its field work five years ago in an effort to bring the jihadists to justice.

"For us, it is absolutely clear that only if we work side by side with Iraqi authorities, in particular with our counterparts in the Iraqi judiciary, UNITAD can be successful," said the UN's chief investigator Christian Ritscher.

The German former prosecutor has been looking into a slew of IS atrocities, from murder, torture and mass rape to slavery and genocide.

He says success would mean that perpetrators of "heinous international crimes" are held accountable "through evidence-based trials and before competent courts."

Among the components needed for success are "admissible and reliable evidence," he added.

"I can assure you that there is no shortage of evidence of ISIL crimes in Iraq," he said, using an alternate acronym for the IS group.

"ISIL was a large-scale bureaucracy that documented and maintained a state-like administrative system."

Because of this, UNITAD launched a huge project to digitize IS documents "to ensure that this evidence is admissible before any competent court, whether in Iraq or in other states."

So far, eight million pages of documents in the possession of Iraqi authorities have already been digitized and are already proving useful in the Iraqi judicial system, he said.

A next step will be "establishing a central archive that will be the unified repository of all digitized evidence," Ritscher added.

In agreement with Iraqi authorities, Ritscher said, the archive will be launched "in the coming days," and will be located at the Supreme Judicial Council of Iraq.

The repository, he added "could be a milestone to founding a comprehensive e-justice system in Iraq which can be upheld as a leading example, not only in the region, but also globally."

After their meteoric rise in 2014, IS jihadists briefly controlled a third of Iraqi territory.

In December 2017, Iraq claimed victory against IS, but it wasn't until March 2019 that the radical jihadist group collapsed, losing its last stronghold in neighboring Syria.