Did the bureaucrats of the Islamic State in Iraq and Syria (ISIS) keep careful records?

Did they flee Mosul too quickly to destroy the written record of their occupation?

Do they care if the world learns more about their atrocities, which they publicized themselves?

We are about to find out.

Collecting, analyzing and disseminating this material will be a major effort, one of the most important as the city is liberated.

The capture of Mosul, Iraq, may produce a potential trove of information about how ISIS organized itself to run a large city. It could assist authorities in identifying those who were its fighters, enforcers and collaborators, and help identify the foreign fighters, enabling countries they came from to head off new terrorist plots. It should offer a record and physical evidence of the ISIS's atrocities, which should be documented, preserved and published.

Collecting, analyzing and disseminating this material will be a major effort, one of the most important as the city is liberated.

Iraqis, for reasons of sovereignty and language, will take the lead, but U.S. and allied intelligence services will be deeply involved and can bring in additional resources and forensic skills and liaison with other services that can quickly check and exploit information.

One objective will be to sort out the population that is liberated from ISIS. ISIS fighters may try to escape the city by pretending to be refugees. Some of those fighters captured or detained may be diehard ISIS supporters; others may have been forced into fighting for ISIS or obliged to do so as a matter of economic survival in a territory without a normal economy.

Who among them can be turned and used for propaganda purposes against ISIS defenders in Raqqa, Syria and elsewhere?

How did ISIS continue to fund its operations, even during the bombing campaign?

ISIS economics is another area of extreme interest. How did ISIS continue to fund its operations, even during the bombing campaign? Who are the corrupt individuals and officials the terrorist organization dealt with in Iraq and abroad?

Iraqi authorities and allies will also want to destroy any left-behind networks or enablers and enforcers of future terrorist undergrounds. Who were the victims of occupation? And who were the willing collaborators? Not all may be written or found. To build a complete picture of the occupation will require extensive interviews among the refugee population.

Another objective will be to learn as much as possible about the identities of foreign fighters who already may have returned to their homelands to set up jihadist undergrounds or wait for instructions to carry out terrorist attacks. How ISIS sends people back and stays in touch with them could be an essential element of information.

Can any of the captured foreign fighters be persuaded to assist in propaganda efforts?

The intelligence analysts should be wary of disinformation. ISIS has had a long time to prepare for the fall of Mosul. It may have destroyed a lot of documents, but it also may have fabricated documents or taken other measures to mislead the intelligence gatherers.

We know that ISIS collects the passports of arriving foreign fighters while fighters infiltrating Europe have used false identities to pose as refugees. The corpses of those killed defending Mosul may be equipped with the passports of foreign fighters to provide cover for ISIS operatives who have snuck back into their home countries.

Investigations should involve photos, fingerprints, and DNA analysis of the dead and fighters captured alive. The captors of Mosul must also be prepared to assess the statements of residents, as locals may aim to settle scores themselves and please the new authorities with denunciations of ISIS, true and false.

These are crimes of war and genocide; future generations may find the only record of their villages and ancestors in museums.

The liberation of the area around Mosul reportedly has already uncovered mass graves of beheaded victims. Retaking Mosul will likely reveal evidence of more atrocities. ISIS's killing fields should be documented photographically, forensically and through testimony; preserved; and published. What happened? How many people were victims? Who gave the orders? These are crimes of war and genocide; future generations may find the only record of their villages and ancestors in museums.

But the issue here is not just the collection of evidence for future prosecution. It is the historical record of an inhumane regime ruled by religious fanatics and foreign thugs attracted by the promise of unlimited violence—an epitaph for its extremism, a discouragement to further radicalization and recruitment, a remembrance for its victims.

Brian Michael Jenkins is a senior adviser to the president of the nonprofit, nonpartisan RAND Corporation, and the author of the recent RAND report "How the Current Conflicts Are Shaping the Future of Syria and Iraq."

This commentary originally appeared on The Hill on November 18, 2016. Commentary gives RAND researchers a platform to convey insights based on their professional expertise and often on their peer-reviewed research and analysis.