Lisi Niesner / Reuters

Survivor Petro Mischtschuk, 87, from Ukraine, wears his old prisoner's garb as he stands near the memorial site of the Little Camp at Buchenwald.

Between July 1937 and April 1945, the Nazis imprisoned a quarter of a million people in the Buchenwald concentration camp, located near the German city of Weimar. Around 56,000 of them were killed before the camp was liberated by U.S troops on April 11, 1945.

68 years later, Reuters photographer Lisi Niesner interviewed some of the remaining survivors as they returned to Buchenwald to mark the anniversary of the liberation.

Lisi Niesner / Reuters

Victor Karpus, 88, from Ukraine, stood at the muster ground where inmates gathered at dawn each day for a roll call. Karpus was imprisoned in several camps including Buchenwald for a total of three years. He even once managed to escape from a camp but got captured and taken to Buchenwald, where he remained until its liberation.

"Work or die – it was impossible to get out from Buchenwald," Karpus says.

Lisi Niesner / Reuters

Lisi Niesner / Reuters

"To each his own": An inscription on Buchenwald's iron gate.

Eva Pusztai, 88, from Hungary, sat in a wheelchair in front of a reconstructed gallows. In July 1944 she was deported to Birkenau and six weeks later to Muenchmuehle, one of 136 satellite camps of Buchenwald.

The forced labor in the arms industry or the camp's stone quarry took the imprisoned to the brink of their physical abilities. "You got just enough food to survive. I lost a third of my weight and I was almost starving to death," she says. 

"The employable have to be destroyed by work," she says, explaining the attitude of the Nazis to their prisoners. Her right eye filled up with a single tear that ran down her cheek, then she composed herself and smiled.

Lisi Niesner / Reuters

"Where is your god? Why he does not help you?" Jakob Silberstein, born in Poland in 1924, remembers the mocking of a high-level Nazi on Yom Kippur. He survived six years of captivity in Buchenwald and Auschwitz and witnessed brutal actions by the SS, being locked in a standing cubicle for a week, carrying stones and drinking rainwater for days. 

He was standing inside the gas chamber at Birkenau when an SS man asked if any of the men were skilled laborers. "I stated I was an electrician, which luckily saved my life," he said. After the liberation he found out that none of his family or friends had survived the war. He now lives in Israel and tirelessly tells his story.

Lisi Niesner / Reuters

Lisi Niesner / Reuters

Urns are displayed in a room adjacent to the crematorium at Buchenwald.

Professor Elling Kvamme, 94, from Norway, stood at the site of Barrack Block 22. He was teaching medicine at a university in Oslo in 1943 when he was arrested for his connections with underground politics. "Students are always dangerous and the Nazis realized it very quickly," he explained.

He was forced to take part in the Nazi program of Germanization and had to work at the pathological facility in Buchenwald. Before the dead were cremated in an incineration system developed to veil the traces of murder, specimens were taken from their corpses for anatomical collections.

Lisi Niesner / Reuters

Vasile Nussbaum, 83, from Romania, spent a year in Auschwitz and Buchenwald. "Buchenwald was a sanatorium in comparison to Auschwitz" he recalls without hesitation.

Nussbaum revisits the site of the camp every year on liberation day. "You never know what’s coming, today we are 83 years old and in the next year we are no more here", he says.

Lisi Niesner / Reuters

Barracks behind trees at Buchenwald.

Editor's note: Pictures taken between April 11-14, 2013 and made available to NBC News today. Read more at Reuters' Photographers Blog.

A German court found John Demjanjuk guilty on Thursday of helping to kill 27,900 Jews at the Nazi death camp Sobibor during the Holocaust. The Munich court sentenced the 91-year-old to five years in prison as an accessory to mass murder as a guard at the Polish camp during World War Two. Defense attorneys had said during the 18-month trial they would appeal any guilty verdict.

Christof Stache / AFP - Getty Images

Defendant John Demjanjuk arrives at the courthouse compound on a stretcher for another session of his trial on May 11 in Munich, southern Germany. John Demjanjuk is accused of helping to murder 27,900 Jews and others during his alleged time as a Nazi death camp guard at Sobibor, one of a network of camps erected by Hitler's Germany in Eastern Europe during World War II with the sole purpose of mass extermination.

Earlier Demjanjuk rejected an offer from judges at the Munich state court to make a final statement ahead of a verdict. Lying in a bed wearing sunglasses and speaking through an interpreter, he replied with a simple "no." Continue reading.

Previous post: Silence in court

Lukas Barth / AFP - Getty Images

The bed of defendant John Demjanjuk is pictured ahead of another session of his trial on May 4 in a courtroom in Munich, southern Germany. 91-year-old Demjanjuk, who is alleged to have been a Nazi camp guard, has been on trial since November 2009.

AP reports: John Demjanjuk's lawyer assailed Germany's prosecution of the 91-year-old on Tuesday, arguing that investigators have failed to offer concrete evidence of his involvement in Nazi war crimes and have been inconsistent in their efforts to pursue suspects.

Demjanjuk is charged with 28,060 counts of accessory to murder for allegedly serving as a guard at the Sobibor death camp in occupied Poland. He denies the charges.

Demjanjuk, as he has for much of his trial, lay in a bed wearing sunglasses during the proceedings. Read more.

International Holocaust Remembrance day marks the liberation of the Nazi concentration camp, Auschwitz, on Jan. 27, 1945.

Janek Skarzynski / AFP - Getty Images

Former prisoners stand in front of the monument commemorating victims of Auschwitz-Birkenau, former Nazi death camp during a ceremony marking 66 years since the liberation of the Auschwitz-Birkenau complex on January 27, 2011 in Oswiecim.

Markus Schreiber / AP

Students pass a red rose at the Gleis 17 (Track 17) memorial at the train station Grunewald on the international Holocaust remembrance day in Berlin, Germany, on Thursday, on Jan. 27, 2011. From Oct. 1941 until Feb. 1945 the train station was one of the major sites of deportations of Berlin's Jewish community.

Markus Schreiber / AP

A man walks along the Gleis 17 (Track 17) memorial with the name of the Nazi death camp Auschwitz at the train station Grunewald on the international Holocaust remembrance day in Berlin, Germany, on Thursday, on Jan. 27, 2011.

Sean Gallup / Getty Images

A survivor of the Auschwitz concentration camps walk through the grounds of the Auschwitz I memorial and former concentration camp on the 66th anniversary of the liberation of Auschwitz on January 27, 2011 in Oswiecim, Poland. Auschwitz was the biggest Nazi concentration camp during World War II and is infamous for its gas chambers where hundreds of thousands of Jews and other victims were murdered.

Menahem Kahana / AFP - Getty Images

People visit the Hall of Names at the Yad Vashem Holocaust memorial in Jerusalem on January 27, 2011.

Oliver Weiken / EPA

A visitor views the Hall of Names in the Yad Vashem Holocaust memorial in Jerusalem, on the International Holocaust Remembrance Day, on January 27, 2011.

Marko Drobnjakovic / AP

People gather in front of a monument at the site of the World War II Nazi concentration camp of Sajmiste, where some 48,000 Jews, Serbs and Roma perished, in Belgrade, Serbia, on Thursday, Jan. 27, 2011.

Baz Ratner / Reuters

An employee returns a box containing tapes to the Yad Vashem Holocaust Museum's archive in Jerusalem, in this August 10, 2010 file photo. A list of confirmed names of Jews killed by the Nazis in World War Two has reached the four million mark, Israel's Holocaust museum announced on December 21, 2010, saying the identity of all six million dead may never be known.

AP says: 

Yad Vashem has made the recovery of the names a main mission in order to keep the memory of the murdered Jews alive.

Yad Vashem says names are recovered through people who remembered the murdered Jews and by combing archival lists and other documentation.

The task is especially difficult because entire families were wiped out and documents were destroyed during the Nazi genocide.

Baz Ratner / Reuters

A visitor looks at a video installation at the Yad Vashem Holocaust History Museum in Jerusalem.

Yannis Behrakis / Reuters

A man stands under pictures of Jews killed in the Holocaust in the Hall of Names at Yad Vashem Holocaust History Museum in Jerusalem.

Menahem Kahana / AFP - Getty Images

Tourists visit the Hall of Names where names and photos of Jews who perished under the Nazi regime are stored at the Yad Vashem memorial in Jerusalem.