The moment I heard it, I knew I had a problem. I had listened to my mother’s Holocaust recollections many times, and now I had hold of my Aunt Ruth’s testimony. And they told an identical tale. Even though Ruth had been six years older than Mum, all the details lined up. Except one. But that one was pretty important.

Ruth and Mum differed on what sort of trains they had been on between their various destinations. They had gone from Amsterdam to Westerbork, then from Westerbork to Belsen and finally from Belsen to Switzerland.

But which was a passenger train and which a cattle truck? Mum’s account was clear, Ruth’s a bit garbled but distinctly different.

How was I to deal with this? I was writing my memoir; I couldn’t just tell the reader I didn’t know. I couldn’t ask either of them, as neither was still alive. I tried official sources, and even the internet, but they were a bit vague. They told me of trains, but didn’t say confidently what sort.

Ultimately, I did work it out. The reason I am telling you all this is that I think the way I solved the problem might help you with learning more about your own family’s story.
Since I published Hitler, Stalin, Mum and Dad, many people have approached me to talk about what happened to their relatives. They often express frustration at how little they know. A fragment here, an anecdote there, but not enough.

There’s no question that I was relatively fortunate as a storyteller. My grandfather was one of the great archivists of the 20th century and this resulted in an enormous amount of carefully preserved paperwork. I also was the son of survivors who talked about their experiences. Many others have relatives who did not survive or who did not talk if they did.

It is also the case that the Dutch Holocaust is much better documented than, say, the Polish one. My grandmother was one of seven siblings in Poland and the only one to survive the war. Of those that died, it proved very hard to find out anything at all about their life or death under the Nazis. Those of you with Polish relatives will definitely find the task harder than I did. And the Soviets, whose oppression was responsible for half of my family story, kept very few records — and still deny the existence of many places of execution and imprisonment.
I was only able to get to the truth because my grandmother survived and kept correspondence.

So my advice won’t work for everyone and it won’t solve everyone’s difficulties, but here is what I did. It’s really very simple.

I realised that anything that happened to my family will have happened to someone else at the same time. So if, for instance, I knew my father was arrested on a particular night in a particular place, there will be many others who suffered in the same way.
Some of those people will have provided testimony, even if your own relative did not. My father was in a traffic jam between his house and the goods station to which he was taken. He didn’t mention it.

Too small a detail, I guess. I discovered this because dozens of others recalled the jam.
My mother always talked about a cruel guard at Belsen who was given the nickname William Tell. I found out more about him because others recalled him too.

So the details of your relatives’ stories are not lost just because they didn’t tell you. Start with even the slimmest fact and you will soon be able to bulk out the story.

And the trains? I found the dates on which they took their various transports and looked for other survivors who might have been on the same journey at the same time. I found a few who left memoirs, but not ones that contained the information I was looking for.

Then, in a privately published book, I happened across a man who had shared the same journey from Amsterdam to Westerbork and had also observed the train my mother had been on. He noted that it was a passenger train and saw fit to include the fact in his memoirs.

Mum, it turned out, had been right all along.

Daniel Finkelstein is associate editor of The Times