The 1994 Rwandan genocide was the last great bloodletting of the century that came to define organized mass killing. 800,000 Tutsis were murdered by their Hutu countrymen, ordinary citizens joining in the killing alongside militia and army. The violence was driven by incendiary politicians and generals. But one global institution stands accused of complicity in the mass killings and protecting some of the murderers to this day.

The Catholic church should have been at the forefront of moral opposition to the massacres. Instead it was virtually silent as churches across Rwanda were turned into human slaughterhouses, compromised by an archbishop closely allied with the politicians behind the genocide. Some clergy courageously resisted the killers but their bishops were not there to back them. Other priests and nuns joined the murderers, overseeing the torture and slaughter of citizens who had turned to the church for refuge. After the violence ended, the Vatican spirited guilty members of the clergy out of the country, and over time, quietly worked them into parishes across Europe.

Chaplains of the Militia is the extraordinary story of those priests accused of complicity in genocide. Chris McGreal takes us from Rwanda in 1994, where he stood among the bodies at one of the many massacres in churches, to modern-day France in pursuit of a priest notorious during the genocide for wearing a gun and selecting victims for the machete-waving militia. He investigates the roots of the Catholic church's complicity in the ideology that underpinned the mass killings, confronting bishops and priests with a past some would rather forget. And, in an echo of the scandal over paedophile priests, he exposes the Vatican's continued protection of clergy with blood on their hands.