It is 60 years since the full horror of the Nazi Holocaust began to emerge with the liberation of Bergen Belsen concentration camp in Germany.
The liberation of Belsen revealed the Holocaust to the world
Belsen was the first death camp entered by the Western allies and first-hand accounts of mass graves, piles of corpses and emaciated, diseased survivors spread quickly around the world.
The BBC's Richard Dimbleby described dead and dying people over an acre of ground, while US radio correspondent Patrick Gordon Walker described the camp as a "hellhole", adding that this was not propaganda but the "plain and simple truth".
But, in the 21st Century, as these events recede into history and the number of Holocaust survivors dwindles, there are still people who deny these crimes happened - and it is a tendency that some experts say is growing.
"Holocaust revisionism is spreading, and not only among neo-Nazis," Kate Taylor, of the anti-fascist publication Searchlight, told the BBC News website.
"As survivors are increasingly dying out it is much easier to hijack history for whatever cause or purpose."
The internet has played a role in this.
COUNTRIES WITH LAWS AGAINST HOLOCAUST DENIAL
While publications peddling Holocaust denial were previously confined to the race-hate paraphernalia of extremist groups, the same material is now readily available on the web.
One of the earliest and most infamous publications denying the Holocaust was a 32-page pseudo-academic booklet entitled Did Six Million Really Die?, first printed in England in 1974.
It dismisses concentration camps as "mythology", rejects the Diary of Anne Frank as a hoax and claims Jews were not exterminated but rather emigrated from Nazi Germany with the help of a benevolent government.
The booklet was widely banned but has resurfaced in electronic form on the internet.
Kay Andrews, of the UK Holocaust Educational Trust, says Holocaust denial sites, subtly questioning the facts, can mislead the young people her group is trying to teach.
"With the internet, you've got to be fairly well-educated to see through what revisionist websites are trying to do," she says.
"I think as soon as you look at them closely you can work it out, but part of the problem that we find is teachers will send pupils off to do internet research and not guide them to specific sites.
"So as a result kids put the Holocaust into a search engine, which comes up with all of this stuff, and at 14-years-old they are not mature enough to make that distinction between a denialist site and a more legitimate site."
However, the eminent British historian Sir Martin Gilbert believes the tireless gathering of facts about the Holocaust will ultimately consign the deniers to history.
"I don't think Holocaust denial is really a problem because of the incredible state of survivor memoirs," he told the BBC News website.
"The number of deniers and the amount of denial literature is miniscule compared with the serious literature, not only the memoirs but the history books, the specialist books, and books which cater for every age group on the Holocaust.
"There is a tremendous range of stuff and some of it is written for young people and teenagers - in that sense the Holocaust deniers have totally lost out."
Over a period of many years, Jerusalem's Yad Vashem museum has documented the lives of more than three million Holocaust victims.
More recently, Steven Spielberg's Survivors of the Shoah [Holocaust] Visual History Foundation (VHF) has recorded more than 50,000 videotaped interviews with Holocaust survivors and witnesses.
But VHF president Doug Greenberg is less confident about the future than Martin Gilbert.
On the positive side, he notes that in 2000 a British judge rejected a libel case brought by a notorious British revisionist, David Irving, against US historian Deborah Lipstadt who had called him one of the "most dangerous spokespersons for Holocaust denial".
David Irving's defeat dealt a blow to the revisionist movement
"The most important thing that's happened in terms of Holocaust denial is the David Irving trial," Mr Greenberg told the BBC News website.
"Because a British court of law said in effect Holocaust denial is not a valid way to look at the past."
On the other hand, he says, we just cannot tell how far history will be forgotten in years to come.
"In 50 years from now, not only will there be no survivors alive, there won't be anybody alive who even knew a survivor, and that is where the real danger lies," he said.
The fear that deniers could gain the upper hand led an SS camp guard, Oskar Groening, to break a lifetime of silence earlier this year in a BBC documentary, Auschwitz: The Nazis and the Final Solution.
"I saw the gas chambers. I saw the crematoria. I saw the open fires. I was on the ramp when the selections [for the gas chambers] took place," said Mr Groening, now in his 80s.
"I would like you to believe these atrocities happened - because I was there."