Viewed from a distance, it is an unremarkable object. Place it on a corner table in any house, and it would probably pass unnoticed, for a while. Picking it up and holding it is another matter. The translucent quality of the material stretched over its eight panels should be attractive but isn't. The lampshade has a curious, waxy texture. You might convince yourself that the covering was some commonplace form of tanned parchment, were it not for its yellow-green opalescence and the fact that embedded in one or two areas of the material are thin, white filaments, slightly thicker than cotton, that have the appearance of very finely minced squid. It seems somehow surprising that it has no smell.

When you run your finger around the edges of a small square that a DNA analyst cut out of one of the panels, you notice the surprising thinness of the taut covering. Leave anybody to examine this object for long enough and I think they would experience two reactions: a slow but mounting repulsion of the kind that occurs instantaneously when you see a rat, and an impulse to ask: "What is this thing made of?"

Before I handled it, I'd been sceptical of the psychological impact this lampshade is supposed to have had on people. Its last owner was troubled by dreams so grotesque that he felt compelled to get it out of his house. His nightmares continued. The lampshade's current proprietor, the American author Mark Jacobson, won't keep it in his home and says that, even now that it's here, safely in storage, he feels more at ease when he knows the shade is shut away in its white cardboard box. The longer I am left alone with it, standing by a window as the daylight is beginning to fade, the more I can understand why.

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"What do you think?" Jacobson asks. "You are aware that the DNA test conclusively states that this lampshade is made out of..."

"I don't think I need to see the DNA test," I tell him.

Witness accounts of such lampshades being discovered at Nazi concentration camps are so common that I'd never questioned the idea that these gruesome ornaments existed. Ilse Koch, wife of the commandant at Buchenwald, was supposedly so partial to such accessories that she was nicknamed "The Lady of the Lampshade". The Holocaust museum at Auschwitz houses two tons of human hair, used by high-ranking Nazis to stuff cushions. The problem for the many who have described seeing lampshades made from people (sources include Allied troops, reporters, intelligence officers and former camp detainees) is that no lampshade fashioned from human skin, of any provenance, has survived as potential support for their testimony. Until now.

Jacobson acquired the lamp four years ago. We have driven for a couple of hours from his home in Brooklyn, across two state lines, to the place where it's kept, safely enclosed in its box, at a location he prefers not to publicise, given the interest, not all of it healthy, that has been generated since his book The Lampshade: A Holocaust Detective Story was published last month.

Jacobson is a highly respected journalist and a contributing editor on New York Magazine. One of his stories formed the basis of Ridley Scott's 2007 film American Gangster, starring Denzel Washington. Jacobson wrote Love Ranch, which stars Helen Mirren as the madame of a licensed bordello. The film opened, to the displeasure of the Daily Mail, earlier this month. Of his novels, Gojiro, whose narrative is observed from the perspective of Godzilla, is rightly considered to be a cult classic. But there's a feeling among his friends that he has never quite found a vehicle which would fully engage his talent as a perceptive, curious and highly intelligent writer; a man well versed in literature and European history with a wonderful ear for dialogue, who is instinctively drawn to subjects that more orthodox writers might dismiss as quirky or even perverse.

In The Lampshade, Jacobson has finally found his niche. It's one of those books – like George Plimpton's seminal Fireworks, or Budd Schulberg's collected writing on boxing – that are powerful and eloquent enough to captivate people with no existing interest in the subject. This last category of reader – The Lampshade being, among other things, about twisted Nazi totemism – is a broad constituency that, until three years ago, included the author himself. Because it was the lampshade, Mark Jacobson recalls, that found him.

"I had a call from my friend Skip Henderson in New Orleans in the summer of 2006," he says. The writer has a second home in the city and, with Henderson, is a member of a group called the Bywater Bone Boys, who maintain a century-old local tradition of rousing Crescent City residents on the morning of Mardi Gras.

"You dress as skeletons, bang on people's windows and shout things like: 'Who next? You next. Rise and shine, predeceased!'" Jacobson explains. "But after Katrina, the joke was over, really. So many people really were dead. It was almost like some force had said: 'You want death? OK. Fine. Have some.'"

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Jacobson was at home in Brooklyn when he took Henderson's call. His friend had just bought a marching drum, stained by flood water, from a yard sale.

"He said the guy he'd bought it from, called Dave Dominici, asked him to look at something else. Dominici said: 'I can tell you will really want this thing.' And he took out the lamp. The stand was modern, but Skip immediately noticed the shade, which was old and had a European fitting. He used to sell vintage guitars and he'd talked to me about how German and other European solder is different in colour from what they use here. He knew the solder on this lampshade wasn't American. Skip asked Dominici: 'What's this thing made of?' and he said, 'The skin of a Jew. Collector's item. $35.'"

Skip Henderson, who "likes to wake up with a story", bought the lamp. He took the shade to an expert in hide-tanning, who said: "The animal this came from never had any fur." The object began to prey on his mind to the point that, in Henderson's words, "Since this thing appeared, it's like my face has been shoved into hell."

At the end of their phone conversation, Jacobson recalls, his friend said: 'Anyhow, it's not really my problem any more.' I said 'Oh, really? Why's that?' He said: 'I mailed it to you, last night.'"

Sitting at the kitchen table, back in his welcoming Bohemian house in Brooklyn, Jacobson recalls how, as a Jewish boy growing up in Queens, he was subjected to cries of "Lampshade" by his less liberal gentile classmates. "That's how well known," he says, "the stories from the camps were."

It was here, in this room decorated by the portraits of the Leeds-born artist Jon Langford, that Jacobson first opened the package.

"I took it out," he tells me. "And I remember thinking: 'Ah. This really does look strange.'"

Antique experts confirmed that the shade's frame is European (to this day, American lampshades differ markedly in their design) and 60 to 80 years old. It has tassels in Mardi Gras colours; these, they said, were attached more recently.

Jacobson took it to a friend, Shiya Ribowsky, a forensic investigator who had worked for 15 years in the New York Medical Examiner's Office, an institution that combines a laboratory and morgue.

"They deal with 12,000 bodies every year," Jacobson says, "8,000 of which are autopsied." '

Shiya Ribowsky is also a cantor at a local synagogue. He observed that the material covering the shade bore similarities to more familiar types of parchment, but was "thinner. Much thinner."

Ribowsky, Jacobson points out, "was working at the Medical Examiner's Office in the months and years following 9/11. More than 22,000 separate fragments of what had once been human beings arrived there during that period. Shiya once told me that working there was 'about as close to Auschwitz as I'll ever get: a total onslaught of death'."

This was the same man who, as Jacobson recalls, "held the lampshade to his face, placed it on the table in front of him, then said: 'This is the saddest thing I have ever seen in my life.'"

"So I asked Ribowsky: 'You don't actually think this is real, do you?' He told me: 'There's only one way to find out: DNA.'"

Shiya Ribowsky sent the lampshade to Bode Technology. Bode, based outside Washington DC, is one of the most highly respected DNA laboratories in the world and conducted much of the forensic work following 9/11. The company is regularly called upon by the FBI and has close links with US intelligence services.

Dr Robert Bever, Bode's vice-president and head of research, told Jacobson that there are two kinds of DNA in every cell. "He explained that there's nucleotide DNA, which is the full ledger of a human being's hereditary dossier, and something called mitochondrial DNA."

Nucleotide DNA yields the kind of unique profile that can send someone to death row. It degrades in the presence of light or moisture. The lampshade was, quite obviously, very old. "And," Jacobson observes, "if there was anything New Orleans had in abundance, besides jazz and drive-by shootings, it was sunshine and humidity."

Bever said Bode would attempt, but not guarantee, to identify the mitochondrial DNA, for a fee of $5,000. "The report came back on 20 April 2007," Jacobson says. "It found a 100 per cent probability that the profile was human. Two human profiles were found, one major and one minor."

It was the judgement of the laboratory that the minor profile might be due to handling, but that the major profile was from the lampshade itself. Dr Bever stated that, on this evidence, he would be prepared to appear in court to testify that the lampshade was of human origin. The skin is that of a white person, or persons; the precise ethnicity cannot be ascertained.

"I think I both wanted and feared that outcome," says Jacobson. "When the guy called me, it wasn't a big surprise. It was shocking. But I was not shocked."

Mark Jacobson headed south to New Orleans, where he found Dave Dominici, who had sold the lampshade to Henderson.

Dominici, Jacobson discovered, was a substance abuser who had served long sentences for stealing from graveyards. "He told me: 'I am not a nobody. I am the famous cemetery bandit.' In New Orleans," the author explains, "bodies are buried above ground, because of the high water table. Dominici stole marble angels, urns and other works of art, from tombs."

It became clear that Dominici, a fan of Nazi documentaries on the History Channel, had no knowledge of the true nature of the object he had sold to Henderson. He lied repeatedly about where he had obtained the lampshade, eventually admitting that he'd looted it from an abandoned house in Lamanche Street, New Orleans.

Jacobson interviewed a woman at the property, without success. "You," she said, "are looking for something that used to be a person. People round here – people that I know – they are looking for people that are still people."

'The Lampshade' is a discursive work consisting of many intersecting themes, one of which is the peculiar resonance between New Orleans – a city with a culture heavily preoccupied with death, even before around 1,500 residents were killed by Katrina – and the morbid practices in the concentration camps. It's an association Jacobson establishes with considerable sensitivity, without elevating or denigrating either group of victims.

He constructs a chilling yet dispassionate portrait of "The Bitch of Buchenwald", Ilse Koch, whose name is only ever omitted from any list of the Ten Most Evil Women in the World through negligence. Ilse, along with her husband, Kommandant Karl Koch, and the camp doctor, Erich Wagner (who was compiling a thesis on tattoos), oversaw a regime that was barbaric even by the standards of the Reich. Numerous former prisoners have testified that she would ride around camp on a white horse, looking for interesting tattoos on the skin of inmates who would then disappear. One survivor from Buchenwald, Kurt Koebess, stated, at Ilse Koch's trial, that he had discovered a preserved section of skin bearing a distinctive tattoo which he had last seen on the torso of a fellow prisoner.

Nine days after the liberation of Buchenwald, a United Press International correspondent named Ann Stringer filed a report saying she had seen a lampshade, "2 feet in diameter, 18 inches high and consisting of five panels made from the skin of a man's chest... I could see the pores and the unquestionably human skin lines."

By the time she was tried in 1947, Ilse Koch had contrived to become pregnant while in custody. Imprisoned for life, she hanged herself in 1967. Koch went to her grave denying that she ever commissioned or handled such a lampshade.

Jacobson tells me that he decided to donate his shade to the United States Holocaust Memorial Museum, in ' Washington DC. It welcomes an average of 5,000 visitors a day, who come to view its chilling installations, and audiovisual accounts recorded by survivors. One film includes footage of the so-called "Buchenwald Table", a collection of shrunken heads and other horrors, among which is a lampshade. It is not Jacobson's.

When he met Diane Saltzman, then head of collections at the museum, Jacobson recalls, "She said that none of the lampshades that have surfaced over the past 50 years have proved to be real," and maintained that the DNA test "proved nothing".

Saltzman argued, said Jacobson, that what she termed "distractions" such as human lampshades had created "fodder for the Holocaust deniers". She suggested, not unreasonably, that further laboratory tests might precisely date the lampshade's frame or stitching, but the Holocaust Museum, which has a private endowment of almost $200m and annual revenue in the region of $80m a year, declined to assist in the process. "Even if you could document this 100 per cent," Saltzman argued, "it would still be a myth."

With no detailed evidence concerning the provenance of his own lampshade, Jacobson, whose engaging, laid-back character belies a tenacious, near-obsessive approach to research, set about disproving the allegation, popular with Holocaust deniers, that no so-called Buchenwald lampshades ever existed.

He chronicles numerous eye-witness accounts, including one from Hitler's godson, Adolf Martin Bormann, son of the Führer's private secretary. The young Bormann, a missionary, recalled a visit to Heinrich Himmler's house. "The furnishings were very strange. There was a standard lamp with a lampshade made out of parchment. And the parchment was made out of human skin."

The sheer volume and detail of such anecdotal evidence was overwhelming, even before Jacobson travelled down to El Paso, Texas, to meet Albert G Rosenberg. Rosenberg, then almost 90, had been the commander of an elite group of American soldiers attached to the Psychological Warfare Division, and was one of the first Allied officers to enter Buchenwald. If Jacobson's book contained nothing more than this one extraordinary interview, it would be worth the cover price.

"When we first came to the camp," Rosenberg tells him, "I had paperwork to do. I sat down at the desk of what was probably some high-up SS man. A French prisoner came and started shouting at me, saying I was no better than the Germans. That I had no shame. Didn't I know the light I was using to write my reports had a lampshade made of human skin?"

Rosenberg adds that, for years, he had kept a piece of preserved, tattooed skin that he'd found at Buchenwald.

"It was a tattoo of a woman with a hat on her head," he tells Jacobson. "It came from a man's chest; you could see the nipple alongside the girl's head." There were, he recalls, "many such objects at Buchenwald. The pathology block was a factory of human skin products."

Rosenberg, a man who, in terms of Allied witnesses on Buchenwald, is regarded as the gold standard, warns Jacobson about the consequences of possessing such material.

Eventually, he says, "I couldn't stand to have the tattooed skin near me any more. I was having so many terrible dreams. I still do. I asked myself, why do I keep this awful thing? But I couldn't quite part with it. I went to psychotherapy for years. I locked it up in a safe-deposit box at a bank but still it haunted me." He gave it to a Jewish friend and told him to dispose of it as he saw fit.

Jacobson's book is much more than an exercise in demonstrating that the Buchenwald lampshades existed. The Lampshade becomes an account of a pilgrimage which takes its author to Germany and Israel, in search of the most appropriate way to dispose of the object, which he takes with him, in its white box. On another level, it's a meditation on mortality and the nature of evil. The narrative includes a number of remarkable encounters, actual or attempted, with such disparate characters as a Holocaust denier, the New Orleans musician Dr John, witnesses of the long agony of the Palestinians on the West Bank, and Ilse Koch's son, now living in Germany.

One interviewee asks him whether the shade was made from the skin of an endangered species. "Endangered?" Jacobson replies. "No. Not endangered. Far from it."

Towards the end of the book, the writer attends a neo-Nazi rally in Dresden, where figures dressed as skeletons, draped in swastikas, raise a banner that reads: "10.5 Million Germans [the approximate number killed in the war] Ask Why?"

"It just pissed me off," Jacobson writes. "'Why? You want to know why? I'll fucking tell you why.' The voice was mine, but it might as well have come from the lampshade itself."

The longer he remains in possession of the relic, the more it seems to unsettle him, mentally.

Skip Henderson, who had long since divested himself of the lampshade, called him from New Orleans, saying he had attended Mass in the city, and suffered some form of temporary mental collapse. "Suddenly," Henderson said, "I felt I was totally attached to everyone who had ever died in a horrible way. I started lighting candles. Candle after candle. I thought they were going to call the police. I had to go out to the park and sit down."

As time went on, Jacobson says, "the lampshade began to prey on my mind, more and more. What does it weigh when you hold it in your hand: a pound? Probably less. And yet all that iconography of death is transposed into this one object."

Jacobson even went to a psychic who, when she saw the lampshade, said: "Oh, they kill him. He says they are all bad to him. They hurt him. They cut him. Stab him with knives." Then, Jacobson says, "She said: 'He wants to stay with you.'"

Jacobson consults Michael Berenbaum, former project director at the United States Holocaust Memorial Museum, ex-professor of Holocaust studies at Clark University in Worcester, Massachusetts, and senior editor of the 22-volume Encyclopaedia Judaica. When the Holocaust Museum was being established, Berenbaum acquired a number of canisters of Zyklon B, the poison gas used by the SS.

The experience of having the canisters in storage in his garage, Berenbaum said, was "enough to send me to psychotherapy".

Berenbaum, Jacobson recalls, "looked at me and asked: 'How long have you had this lampshade?' 'Several months.' 'Months? Here's some advice. Being around these things, thinking about them, can drive people out of their minds. I'd get as far away from it as I could.'"

"It can't have felt good," I suggest to Jacobson, "travelling with that thing. Sharing bedrooms with it."

"No," says the writer, who recalls that, in one hotel room, he found himself talking to the lampshade. As the book goes on, the narrative is increasingly coloured by his own psychological relationship with the object.

"Do you think the lampshade's possible history began to disturb the balance of your mind?"

"Perhaps some lunacy did start to creep into me during that period, but I felt that giving in to it would be a shirking of duty. As for talking to the lampshade, it seemed only natural after a while. I probably shouldn't have referred to it by name ['Ziggy']. I had moments of terror, there's no doubt. But after a while the horror went away and sympathy for the poor individual – I always thought of it as one individual – took over. I spent so much time with it. There were days when, any time I took it out of the box, I didn't have a good night's sleep. But gradually – I know this sounds horrible – I got used to it. In my mind, it somehow altered from this symbol of evil to a very sad image of death."

On his travels, Jacobson encountered a wide range of conflicting advice on what best to do with the lampshade. Some argued that it must go to a museum, because the Holocaust should not be censored. Others, like Berenbaum, insisted that putting such objects on display could be regarded as a form of pornography. Jacobson found an Israeli museum which was prepared to exhibit the lampshade, but the place was run down and slightly shabby. In one of the most anthropomorphic passages in the book, he explains that he didn't feel comfortable leaving "Ziggy" there.

One Orthodox rabbi told him to bury it.

"He felt this would be in keeping with Jewish law. There is a group that goes around, after every suicide bombing, and buries every last piece of Jewish flesh, down to each drop of blood."

Another told him not to.

"Jewish law states that non-Jews are not supposed to be buried in Jewish cemeteries," Jacobson says, "and we don't know if the person, or people, whose skin was used in this lampshade, are Jewish. The fact that the DNA report was inconclusive on this point is very important to me. It is a human being, but we don't know quite what kind."

Of the Roma people held in the death camps, Jacobson points out, at least 250,000, possibly half a million, died.

In the end, the writer says, "I decided I didn't want to bury it because, whatever 'it' is, it doesn't belong to me. As a journalist, when something of this kind arrives at your door, what are you supposed to do? Ignore it? The hard thing to explain to people is that you only need to take one look at that lampshade. I immediately felt – like you did – that it has this weird aura about it. I was trying to translate its message. That is what this book is about. While I was writing it, I even felt a sense that this was what I was supposed to be doing with my life."

Jacobson may be speaking in the past tense here, but I am not sure that, even now, he is entirely confident that his emotional connection with the lampshade has been severed, or that his duty as custodian of the relic has been fulfilled, however far away the object is secreted.

Further testing might be undertaken, as Diane Saltzman suggested, which could identify, more precisely, the age and origin of the stitching and frame. It's more than likely that the individual from whose property it was stolen, or somebody claiming that identity, will surface in New Orleans, given the wide publicity that The Lampshade has already attracted in the United States.

Of all the discomforting aspects of Jacobson's recent experience – and there are a few – this may be the most troubling: a lingering suspicion that this remarkable story is not quite over.