There have been times over the years when I've tried to make some sense of the Rwanda genocide. I've considered Belgian colonialism, demographic pressures, radio propaganda, political culture, and so on. But always these thoughts give way to recollections of driving throughout that beautiful, cursed country two decades ago.

I recall relaxing, after a long day of negotiating roadblocks, on the veranda of the home of a Bosnian missionary, the bravest man I ever knew, sipping from a bottle of orange Fanta. The feeling at dusk was pure rural Rwanda: green-gray hills fading in the gloaming and the sweet scent of burning eucalyptus wood. But the sounds were different. No end-of-the-day chatter coming from the huts below us, but instead the dull, distant thunder of heavy artillery. My friend's brother was a sniper back home in the Balkans; the missionary himself would later be assassinated in the streets of Kigali.

The first dead person I saw was lying on his back in the grass of a gently sloping meadow just off the main road between the Burundian border and the pretty university town of Butare. He was wearing only a pair of khaki shorts; perhaps he'd been hoeing his field in the hot sun, or maybe roughly awakened from a sound sleep. He had been of average size, but when I saw him he was swollen and bloated, and he looked absurdly portly. His face, though, was like a badly used black soccer ball, with the stitching coming apart.

Later I saw more.

A father and his small son lay in the middle of a well-paved road late at night, my headlights illuminating the dark blood pooling around their embracing bodies. The killer peered for an instant from the tall grasses on the verge, holding a spear and wearing a macabre crown of banana leaves.

Elsewhere victims were dried, almost mummified, when I came across them, splayed out in the doorways of their houses, hanging from windowsills, and strewn across an overgrown flower bed.

But usually the dead were only noticeable by the faint traces they left behind. Often they revealed themselves in a moist, moldy smell seeping from the loamy soil of isolated banana plantations. It's not an odor I can describe, but it's one that's hardwired into my brain. Or in the courtyard of a building, one would simply come across a random pile of shoes, flip-flops, and, worst of all, photo-ID cards with the faces of men, women, and children who no longer existed. They couldn't have known what terrible things life held in store for them, but their sad eyes suggested that this was all somehow inevitable.

The dead were tragic and haunting, but it was the living who worried me most.

A tall Hutu peasant stood at an informal roadblock, the kind of place where Tutsis were identified and taken into the woods for slaughter. He wore a shabby trench coat with sleeves too short for his strong, knobby wrists, one of which held a club studded with nails. "To deal with the Nilotics," he explained, referring to the Tutsis.

Then there were the government functionaries, the police officers, the customs officials, putting on their uniforms and going to their workplaces, carrying on the farcical routines of administration, when we all knew there was only one real business to be conducted. The phrase banality of evil is overused but sometimes makes perfect sense.

There are doubtless important economic, social, and political lessons to be learned from the Rwandan genocide, and perhaps some day we might even learn them. For me, though, there is only one lesson:

A terrible thing lives in us all, and the struggle to be human is essentially the struggle against that beast.

Chris Hennemeyer is an international development consultant who served as the director of Catholic Relief Services' program in Rwanda during and after the genocide.