In the last days of June 1941, Nazi Germany drove the forces of the Soviet Union, its former ally, out of eastern Poland. By 10 July the Russians were gone from the small town of Jedwabne. On that day, hundreds of Jewish people whose families had lived there for centuries were killed.

The younger men were clubbed to death. Older people, and mothers with children, were driven into a barn that was set alight, burning them to death. When the Soviet Union regained control of the area an investigation into the massacre was ordered and a memorial was erected, announcing that 1,600 Jews had been killed there by the German Gestapo.

It wasn’t until 2000 that this version of events was challenged publicly by the Polish-American historian Jan Tomasz Gross in his book Neighbours. “One day, in July 1941,” Gross wrote, “half of the population of a small east European town murdered the other half.” The killers, in other words, were not the German invaders, but the Polish inhabitants of Jedwabne.

His book triggered a furious controversy. The Polish president went to Jedwabne and led a service of commemoration and atonement: the people of the town stayed away and the mayor, who had planned the ceremony, was forced to resign.

The Polish Institute of National Remembrance investigated. Four years later, it concluded that the German authorities had, at least tacitly, signalled “permission to commit the crime”, that there were probably Germans present on the day of the massacre – most likely only three or four of them – but that the perpetrators were local Polish people. The number of victims was probably nearer to three hundred than sixteen hundred. But the substantial fact remains that at least 40 Polish men, from Jedwabne and areas nearby, had assembled in town on that day, of their own free will, with the clear and premeditated intention of killing the town’s Jews. The rest of the townspeople stood by and let it happen.

When Gross’s book came out Anna Bikont, a journalist with one of the leading newspapers in Poland, determined to go to Jedwabne to find out more. Her editor was not enthusiastic. A friend of Bikont’s, a poet, asked her what she thought she could add to a story that Gross had already so sensationally revealed. This book, first published in Poland in 2004, is an answer to that question.

Its form is idiosyncratic. There are stand-alone essays (on anti-Semitism in the pre-war Polish church, on the Soviet occupation) and there are individuals’ stories, based on interviews. At least half of its bulk, however, consists of entries from Bikont’s journal, kept during the four years of her work. They are as bitty and unguarded as a private journal usually is.

Any researcher, starting work on a project, amasses information that initially makes no sense. Beginning in ignorance, you are easily fooled. You come across stories presented as factual, which are in fact parables whose significance becomes evident only as your understanding of the political and cultural context deepens. If, as in Bikont’s case, you are talking to frightened, senile people who were children at the time of the sixty-year-old events you are trying to understand, the narratives you glean will be unreliable, and mutually contradictory.

As Bikont gives us much of her material in the order in which she found it, without recasting it in the light of what she eventually learned, readers stumble through this book as confused as she was. One cannot comprehend what went on in Jedwabne without knowing the chronology of the district’s wartime occupations by Soviet Russia and then Nazi Germany; Bikont does not provide that framework.

Poles alleged that during the Soviet occupation their Jewish neighbours had denounced them to the NKVD (in fact, only a handful of Jews collaborated): it is not until nearly a third of the way through the book that Bikont tells us about this. Nor does she directly describe the town’s social structure; it is only by inference that readers will gather that many of the Jews’ killers were their employees or their debtors. There are repetitions. Characters appear and reappear without ever being introduced. Inconsistencies are passed over unremarked. Important themes emerge too late to illuminate our reading – the place of property in this story, for instance. Polish people took over the houses of the dead Jews; now their heirs fear being asked to hand back those houses, or to pay compensation. It is as though Bikont, in a hurry to get the book out, had simply handed over her raw material. Cooking would have improved it.

An advantage of her unmediated account, however, is the directness with which we sense how alive this story still is. Visiting Jedwabne, Bikont finds people hovering threateningly around the houses of those who have talked to her. Many refuse to open the door to her. Discovering that she is Jewish, some recoil; others, meaning to be kind, promise not to tell anyone. She parks her car in shadowy corners and waits between appointments with the windows wound up and the doors locked. Her heroine, a Polish woman who hid seven Jews in a dugout beneath her pigsty, worked for many years afterwards as a cleaner. She never told her employer that she had been invited to Israel to be honoured as one of the “Righteous Among the Nations”. Better, in Jedwabne still, not to talk about such things.

Bikont’s journal makes her a character in the story – a likeable character, but all too human. She candidly confesses to her failings as a reporter. She allows interviewees to ramble on self-justifyingly for hours. She cannot bring herself to ask the crucial question: “What did you [or your father] do on 10 July 1941?” She notes down testimony and her own impatient responses: “Idiocy!” “This is ridiculous!” She is sarcastic about those with whom she disagrees. A finished text would have to sound authoritative, judicious. Because so much of this book is presented as unrevised jottings from her private notebook, she allows herself to be intemperate in her snap judgements and shrill in her indignation.

The author intervenes in the story she is reporting. She attends the funeral of Stanislaw Ramotowski, an old man who saved a Jewish family. The priest’s eulogy is bland. Bikont takes the microphone and pays tribute to the dead man for his courage. Afterwards his nephew says to her, “You seem not to understand the situation. Stanislaw was a respected and liked person here . . .” Now, because of her insistence on telling the truth, the nephew is jeered at as he walks down the street – “Jew”. Bikont is undeterred. It is she who urges the mayor to take a stand, thereby causing him to lose the office. People who have helped her get anonymous phone calls late at night: “Dirty Jew!”

She goes to America and visits Rabbi Jacob Baker, a co-editor of the Jedwabne Book of Memory. She doesn’t have the heart to tell him that the accounts he presents of victims embracing and kissing each other as the flames rose around them are “no more than edifying and moralising fairy tales”, but she concurs with his view that the facts must be told – that to connive in a cover-up is to murder the murdered a second time.

There are horrors here. Women drowning themselves and their babies in muddy puddles rather than fall into the hands of persecutors. Heads and limbs hacked off. Children thrown into the fire. The weird, theatrical pathos of the procession to the barn on that awful day in July 1941, when the Jewish men of Jedwabne were forced to smash the town’s statue of Lenin and then carry its fragments to the place where they would be killed, their rabbi in the lead, carrying his hat on a stick, all singing “The war’s our fault”. These are terrible images, and in Bikont’s incoherent narrative they recur, with variations, which gives them a disturbing extra quality, like a nightmare from which one cannot wake up. But the main value of her book lies not in what it adds to what her sometimes unsure translator calls “the Holocaust business”, but what it has to say about anti-Semitism in Europe seventy years later.

There may be many more such stories to be told. At the Worlds Literature Festival in Norwich this summer I heard the Lithuanian writer Sigitas Parulskis talking about his novel Darkness and Partners (not yet published in Britain). It tells of the massacre of Jews in rural Lithuania, instigated by the occupying German Nazis but largely carried out by local, anti-Semitic collaborators. Some Lithuanians have accused Parulskis of “obscenity”. They do not want to think about such things. Like the Poles, they particularly do not want it said that their own compatriots were at least partly responsible.

It is hardly possible to exaggerate the guilt of the Nazi regime, but not all of the wartime crimes committed in eastern Europe can be laid at its door.

The Crime and the Silence by Anna Bikont is published by William Heinemann (544pp), £20