The bells of a church in Bartella rang out last week for the first time since 2014. That was the year ISIS captured the town which lies 13 miles to the east of Mosul in northern Iraq. When the black-clad fighters entered Bartella they tore down crosses, hung their flags from church walls and ordered the few remaining Christians to either convert, pay an extortionate tax or face “death by the sword”.

No one, sadly, will have heard the bells of Bartella in the streets of Mosul. Currently residents of Iraq’s second city can only hear the hellish din of war: missiles, mortars, suicide bombs and bullets. As Pope Francis put it in his Angelus address on Sunday, “Our souls are shaken by the brutal acts of violence that are being committed for too long against innocent citizens, whether Muslims or Christians.”

But the moment is surely coming when the silenced bells of Mosul will ring out too. Christians lived there continuously for 1,600 years before the arrival of ISIS. Mosul even has a place in our salvation history: across the River Tigris lie the ruins of the biblical city of Nineveh. We hope that Mosul’s empty churches will soon be full of worshippers once again.

When ISIS loses its last major foothold in Iraq – and it will – investigators must document the terror group’s crimes as quickly as possible. If there is any delay, we may lose crucial evidence of ISIS’s genocidal activities. For ISIS is no ordinary Middle Eastern dictatorship; it is arguably the most barbarous regime since Nazism. We must treat it with the same severity: defeating it thoroughly on the battlefield and then prosecuting what remains of its leadership.

The prospect of ISIS leader Abu Bakr al-Baghdadi standing in the dock at The Hague may seem remote. But that is what we must aspire to if we want to send an emphatic message that no one can slaughter hundreds of thousands of people and get away with it.

Amal Clooney, a distinguished human rights lawyer whose actor husband you may have heard of, is one of the few seeking to bring ISIS to justice. In a forceful speech to the United Nations last month, she pointed out that “not a single member of ISIS has been prosecuted in a court anywhere in the world” for genocide against Yazidis. “I am ashamed as a human being that we ignore their cries for help,” she said. “We know that what we have before us is genocide, and we know that it is still ongoing. We know exactly who the perpetrators are. ISIS brags about its crimes online.”

​How to continue reading…

This article appears in the Catholic Herald magazine - to read it in full subscribe to our digital edition from just 30p a week

The Catholic Herald is your essential weekly guide to the Catholic world; latest news, incisive opinion, expert analysis and spiritual reflection