Palace of Justice, Nuremberg, 20th November 1945

I always wanted to know exactly how my father had managed to escape from Nazi-occupied Poland and survive the Holocaust that killed almost his entire family.

Like so many other refugees trying to build a new life in a foreign land, he didn’t want to talk about the past he’d lost for ever. When my father reached his early seventies, though, he seemed more willing to open up. Thinking he’d find it easier to talk to a stranger, I arranged for a fellow journalist to interview him. There seemed no particular hurry. And then my father suddenly died. Even though I used to carry a BBC tape recorder on my shoulder for a living, I found I didn’t even have a recording of his voice—let alone an account of his life.

When my son was two, his grandfather died. So, after university, he set off for Poland to find out about the grandfather he never knew. To my amazement, he was able to trace the Rozenbergs of Izbica as far back as the 18th century. He also discovered that my father had been deported to the Soviet Union before enlisting in the Polish forces under British command in Iran. That was followed by the British Army, naturalisation and a return to his pre-war occupation as a tailor.

Researching and publishing our family histories allows European Jews to demonstrate—in a way that readers can readily comprehend—the ultimate failure of Adolf Hitler’s attempt to wipe us all out. It is a well-trodden path. In his new memoir My Dear Ones: One Family and the Final Solution (William Collins), Rabbi Jonathan Wittenberg consults the German Holocaust researcher Götz Aly. “Many people come to see me with their enquiries,” Aly tells him. “They almost all have one thing in common: they’re over 50, mostly over 60, and those from whom they could once have enquired are dead.”

But there are two things that make the family story of the lawyer and author Philippe Sands stand out from the rest of the genre. First, his assiduous research has enabled him to construct entire chapters of East West Street: On the Origins of Genocide and Crimes Against Humanity from a flimsy scrap of paper or an unidentified photograph. Those interspersed passages, which bring the book alive at the cost of making the narrative harder to follow, read more like a thriller or a spy story: not many barristers have their books endorsed by John le Carré. Sands was surprised to find that the survivors he tracked down seemed uninterested in what he had found out about their families. But I now begin to understand why they would rather not know.

“Crimes against humanity sound so familiar to us now, but think how revolutionary they were 70 years ago”

Second, the author has uncovered extraordinary personal coincidences. We may imagine that we choose our careers; but developing and teaching the laws of genocide and crimes against humanity was clearly Sands’s destiny. His maternal grandfather lived in the same city as the two Jewish lawyers who competed to conceptualise international criminal law: the very law that was used to convict those responsible for murdering some 70 of his grandfather’s relatives; and those lawyers’ relatives; and millions more like them.

That city is now Lviv, in western Ukraine. During the 20th century it was, successively, Austro-Hungarian Lemberg; Lwów, in Poland; Soviet-occupied Lvov; and then Lemberg again under the Nazis. Sands’s grandfather Leon was born there in 1904.

The lawyers who came to live and learn in Lemberg were Hersch Lauterpacht (1897-1960) and Rafael Lemkin (1900-1959). Of the two, Lauterpacht was to become the better known, ending up as a QC and the UK’s judge at the International Court of Justice—even though the Attorney General at the time would have preferred someone “thoroughly British.” Lauterpacht was born in the nearby town of Zółkiew and lived on the same east-west street as Sands’s great-grandmother. His son, born near Sands’s home in London, is Elihu Lauterpacht QC, himself a highly distinguished international lawyer. Lemkin taught in the United States after the war but never married and left no children.

Sands visited Lviv for the first time in 2010, when he was invited by the university to give a lecture about the origins of international law. Nobody he met there knew that two of the university’s former students had between them done more than anyone else to create the modern system of international justice. Indeed, the only person who realised that these pioneering rivals had each studied at the same law school under the same teachers (although not at the same time) was Sands himself. Why did nobody talk about Lauterpacht and Lemkin at the Lviv law faculty today, one student asked. Another took Sands aside and told him the answer he must have known only too well. It was because they were Jews.

Shrewdly, a student asked Sands the legal question that has become the theme of his book: the difference between crimes against humanity and genocide.

“Imagine the killing of 100,000 people who happened to come from the same group,” he explained, “Jews or Poles in the city of Lviv. For Lauterpacht, the killing of individuals, if part of a systematic plan, would be a crime against humanity. For Lemkin, the focus was genocide, the killing of many with the intention of destroying the group of which they were a part.”

From a prosecutor’s point of view, a crime against humanity is easier to prove. To establish genocide, you need to show that the killing was motivated by an intention to destroy the group. That may be difficult to prove in modern tribal conflicts, where evidence is hard to come by. But what about the Nazis? Surely there was ample written proof of their planned Final Solution?

That was always Lemkin’s view and it deserves to be taken seriously—not least because it was Lemkin who coined the word genocide, joining the Greek for “tribe or race” to the Latin for “killing.”

His research into Hitler’s genocide had begun in 1940, while the lawyer was waiting in Sweden for his United States visa to come through. Lemkin spent his time collecting Nazi decrees and ordinances, studying them for underlying themes and objectives. His work “identified the wholesale destruction of the nations over which the Germans took control as an overall aim,” writes Sands. “Lemkin identified decrees from early 1941 pointing to the ‘complete destruction’ of the Jews in ‘gradual steps.’ Individually, each decree looked innocuous, but when they were taken together and examined across borders, a broader purpose emerged.”

But Lauterpacht was sceptical. “He thought genocide was going a bit too far,” his son told Sands. Elevating the role of groups would undermine the protection of individuals. It was also impracticable.

Sands traces Lemkin’s efforts to have genocide recognised by the international military tribunal that sat at Nuremberg from 1945 to 1946. There was some support from Robert Jackson, the US Supreme Court justice appointed as chief prosecutor. But, to his huge disappointment, Lemkin was excluded from Jackson’s legal team—apparently because he was so emotional and unmanageable. He managed to get his neologism into the Nuremberg indictment, though only as as a subset of “war crimes.” Leading Nazis were accused of “deliberate and systematic genocide,” defined as “extermination of racial and religious groups.” But there were no convictions for genocide. The term was not even mentioned in the tribunal’s final judgment.

Lauterpacht, by contrast, became a key figure in the prosecution team and his thinking was reflected in the tribunal’s verdicts. Shortly before the indictment was finalised, Jackson had visited Cambridge, where Lauterpacht had been professor of international law throughout the war. Over tea and cake in the garden, the professor suggested a compromise that might resolve differences among the allies over the charges that the Nazi leaders should face. What about introducing a new term into international law to address atrocities against individual civilians, Lauterpacht asked. Why not refer to those atrocities as “crimes against humanity”?

Within just a couple of weeks, agreement was reached and the crime had become part of international law. A year later, 16 men were found guilty of crimes against humanity. All but four were sentenced to death.

It’s because genocide and crimes against humanity sound so familiar to us now that we should pause and consider how revolutionary they must have been 70 years ago. Here, for the first time, were limits to the absolute power of a sovereign state. No longer would a nation be free to treat its people entirely as it wished. No longer could its leaders act with impunity.

And might concepts such as crimes against humanity and genocide deter the tyrants of the future? Those were my hopes in the summer of 1998 as I filmed for BBC news in Sarajevo. The capital city of Bosnia and Herzegovina was still scarred from a siege by Bosnian Serbs that had lasted almost four years. My producer and I found tiny fragments of human bone in the killing fields. After all flights out of Sarajevo were cancelled, the taxi driver we persuaded to take us to Zagreb made a brief detour to kiss his wife and children goodbye—fearing he might not return.

We had to be in Rome for the start of a conference that was intended to put an end to wars against civilians. The International Criminal Tribunal for the former Yugoslavia was already trying leaders accused of crimes against humanity but its remit was limited in time and place. In approving the founding statute of the International Criminal Court (ICC), the 120 nations who gathered in 1998 were creating a court with no such limitations.

The Rome statute received the required 60 ratifications in record time and the court assumed limited jurisdiction in 2002 to try and punish individuals for the crime of genocide, crimes against humanity and war crimes. Lemkin would have been proud to see his crime listed first. Genocide was defined to include “acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group.” Crimes against humanity included acts “committed as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack.”

The ICC was a revolutionary development and one I welcomed. But my enthusiasm for the court turned sour when its prosecutor, Luis Moreno Ocampo, took nearly nine years—almost his entire term of office—to secure his first verdict.

Thomas Lubanga, a warlord from the Democratic Republic of Congo (DRC), was found guilty in 2012 of “conscripting and enlisting children under the age of 15 and using them to participate actively in hostilities.” Without wishing to diminish its importance, this was hardly the most serious crime in the Rome statute.

And yet the prosecution was beset by difficulties throughout. The three trial judges, headed by Adrian Fulford, were highly critical of the prosecutor’s decision to delegate his investigative responsibilities to locally recruited intermediaries—mainly human rights activists given the job of tracking down the former child soldiers. A number of these intermediaries were alleged to have suborned witnesses and, as a result, some of the evidence proved unreliable.

Thomas Lubanga, a Congolese warlord, hears the first sentence delivered by the International Criminal Court on 10th July 2012 after being convicted of war crimes ©Jerry Lampen/AFP/Getty Images

Lubanga was sentenced to 14 years in prison, nearly half of which he had already spent awaiting trial. He is now serving his sentence at a prison in the DRC. In 2014, his compatriot Germain Katanga was convicted by the ICC of war crimes and crimes against humanity—in his case, murder. Katanga’s sentence was reduced on appeal and he has now completed it. A co-defendant was acquitted.

The ICC delivered its fourth verdict in March, convicting Jean-Pierre Bemba, a former Vice President of the DRC and previously a leader of a Congolese rebel group that committed widespread atrocities in the neighbouring Central African Republic. Bemba’s conviction for war crimes and crimes against humanity broke new ground by focusing on the use of sexual violence as a weapon of war. His militia had gone from house to house, raping the occupants.

After 14 years, the ICC has begun to show that it can operate as a court. But what it has singularly failed to do is to act as a deterrent. It means nothing to the world’s worst war criminals, such as the Syrian President Bashar al-Assad. It means nothing to the leaders of Islamic State. It meant nothing to Muammar Gaddafi in Libya or Saddam Hussein in Iraq. And it does not even seem to bother Omar al-Bashir, the President of Sudan, who was allowed to leave South Africa last year despite being wanted by the ICC on counts of genocide, war crimes and crimes against humanity in Darfur. By signing the Rome statute, South Africa had agreed to enforce ICC arrest warrants.

Inevitably, politics have intervened. Some African leaders believe the ICC has unfairly singled out crimes on their continent for investigation and prosecution. Other critics are not assuaged by the nationality of Moreno Ocampo’s successor—Fatou Bensouda is from Gambia—or by her decision to drop charges against President Kenyatta of Kenya and his deputy.

As my initial enthusiasm for the world’s first permanent international criminal court turned to despair, I recall talking to Sands about Moreno Ocampo’s failings. He urged me to take the long view, assuring me that international justice took time to gain acceptance.

In his book, he recounts some of the milestones that followed. The ICC has charged a serving head of state with genocide—even though al-Bashir is still at large. At another international tribunal in 2012, Charles Taylor, the former president of Liberia, was sentenced to 50 years in prison for crimes against humanity.

In 2007, the International Court of Justice ruled that Serbia had violated its obligations by failing to prevent genocide in Srebrenica. That was the first occasion on which a state had been condemned by an international court for violating the international convention on the prevention and punishment of genocide—Lemkin’s lasting memorial. There is no such treaty yet on crimes against humanity.

Sands remains uncomfortable with the concept of genocide, arguing that by pitting one group against another the charge makes reconciliation less likely. “It enhances the sense of solidarity among the members of the victim group,” he says, “while reinforcing negative feelings towards the perpetrator group.”

But these victim groups are not clubs that members may join or leave at will. The loyal and assimilated Jews of Germany who were murdered by the Nazis considered themselves more German than Jewish. Hitler was indeed guilty of genocide.

And where does this leave Sands himself? He discovers that his mother owes her life to a devout Christian who brought her out of Austria as a baby, a woman whose mission was to save the Jews. All he tells us of his father is that Ruth, brought up in France, “married an Englishman.” Though they gave their son a French name, it keeps alive the memory of his great-grandfather.

The author of this revealing book now knows as much as anyone could discover about his Jewish forebears. But however many archives he searches, his own identity still eludes him. To which group does Philippe Sands belong?