One of the hardest things about hearing people's stories in Iraq of rape, persecution, violence and beating was knowing that these were the people who had got away. The many families I met in the Kurdish region of Iraq who had fled shootings and the risk of sex slavery were just that – the ones who had fled.
And of course, thousands of people didn't. I haven't watched any of the Internet clips showing executions – described by one commentator as 'atrocity porn' – but we all know that it's happening. As, apparently, are the sex slave markets.
A number of people in different cities told me of the systematic rounding up of women and girls; the rapid, enforced divorce of married women from their husbands; the 'testing' of single women to assess whether they're considered to be a virgin; the colour-coding by clothing of married and single women;
the selling in an open market with virgins commanding the highest price; and the hasty marriage ceremonies between buyer and the woman they've bought in order to justify his raping her. And these are not just grown women.
The youngest girl we heard of being taken for rape was three years old. I heard about the sex slave markets from a number of people – men, women, Christians, Muslims. One Muslim man told me: "I don't know where they found an imam to do the marriage ceremonies. No imam I know would do it. This is not being done in our name."
So it's not surprising that people leave. Since January 2014, 1.8 million people in Iraq have left their homes. The movement intensified from June when ISIS took Mosul and then in August, when ISIS issued an edict to non-Muslims giving them 48 hours to convert or die, 600,000 people left areas like Mosul.
Those with financial and physical strength go far and they go fast. They take their passports, get on a plane and go to a different country. It happens every time there's fighting on this scale and people become displaced. Those with means leave before it gets worse.
We saw it in the Syria crisis and in many of the other conflicts where Tearfund has served displaced people over the last 45 years. The most vulnerable people remain close to the area from which they came – whether they're internally displaced in Iraq or crossing the border from Syria into Lebanon or Jordan.
They're vulnerable for various reasons. Usually, we see families with disabled children, elderly relatives or large numbers of extended family travelling with them. They're often financially less well-off than those who can travel further away, so they have lots of needs.
And then those who have cars, friends in other cities or in neighbouring countries, and have managed to hold on to their ID documents during the raids, will go. They manage to travel further than their more vulnerable neighbours.
But the journeys, even for those with cars, are hard. One 45-year-old mother told me of lying on the floor of her car with her children as they listened to the bullets flying overhead. Opposing groups were shooting each other over the roof of her car.
They made it to Erbil, where they now sleep on the floor of a church with 30 other families. Compared to what they've escaped, their lives are relatively safe but in no way comfortable.
They need water, food, more permanent shelter and, very soon, a livelihood so that they can rebuild their lives and avoid becoming dependent on what little provision there is available to assist unemployed people.
They're determined, resilient, grief-stricken and traumatised – all at the same time. But they're forever grateful. They know they're the ones who got away.
Katie Harri works for the charity TearFund