Tucked away in the picturesque German city of Ludwigsburg, a tiny team of investigators tracks the last surviving Nazi war criminals across the globe and through the better part of a century, in an urgent race against time.
"We put together the smallest pieces of information, like the pieces of a puzzle, to work out who was employed in what role, from when until when" in Adolf Hitler's totalitarian killing machine, says prosecutor Jens Rommel.
He has since 2015 led the eight-strong Central Office for the Investigation of National Socialist Crimes, at a time when the last perpetrators, accomplices, witnesses and survivors are finally vanishing.
Once all the perpetrators are gone, Germany will close the judicial side of its coming-to-terms with the Nazi government's extermination of six million Jews and hundreds of thousands of others in the Holocaust.
In the meantime, the spectacle of frail defendants aged in their 90s appearing in courtrooms to answer for crimes dating back to 1945 or earlier has renewed vigorous debate about the country's dark history.
For decades after the war, the German government and justice system showed little haste to track down many of those involved in the organised mass murder.
A landmark change came with the 2011 sentencing of John Demjanjuk, who served as a guard at the Sobibor extermination camp in occupied Poland in 1943, to five years in prison.
The ruling opened the way to prosecuting anyone who worked at a concentration camp -- from soldiers to accountants -- as an accomplice in mass murder.
Before that judgement "we never cast an eye over the smallest cogs in the machine," said lawyer Andrej Umansky, author of a book on the Holocaust in Eastern Europe.
The changed legal landscape since then, he said, offers a chance "to give victims a voice, their families, and to bring the facts back into the public consciousness".
- From Moscow to Buenos Aires -
The team's probes into the dust-shrouded past have taken Rommel's team of five prosecutors, two judges and one police officer across the world in search of their quarries.
Many German Nazis fled to South America immediately after the war, among them one of the main architects of the Holocaust Adolf Eichmann, who landed in Buenos Aires.
He was captured by the Israeli secret services in 1960 thanks to information passed on by German prosecutor Fritz Bauer, who was outraged by the inching progress of his own country's justice system.
As for less notorious Nazis, "all the boats that arrived there were registered. We have combed the passenger and crew manifests" and followed up on any German-sounding names, Rommel said.
Officials scoured immigration registers, applications to be naturalised in Argentina, and the records of the German embassy.
"We owe it to history" and to the millions of victims to "battle against forgetting", said Peter Haeberle, of the justice ministry in Baden-Wuerttemberg state, where Ludwigsburg sits just outside its capital, Stuttgart.
The team's travels halfway around the globe -- at a time when there remains no chance of tracking down a living high-ranking Nazi official -- have not escaped criticism in the press, such as from Die Welt daily, over their sometimes exorbitant cost.
- 1.7 million files -
Many have criticised the comparatively small number of Nazi war criminals ever brought to justice.
By 2012, some 6,498 people had been convicted for their part in the Holocaust.
The monumental weight of history is clear from the smell of aged paper lingering behind the security doors of the former women's prison where the investigation team is based.
One million seven hundred thousand cardboard files are stored in rigorous alphabetical order in rows of imposing metal cupboards -- a unique full-size database of Nazi criminals and details of their acts.
From Hitler to the lowliest soldier or helper, every Nazi wrongdoer identified up until the present day is recorded here, along with the places of their crimes.
Rommel carefully withdraws file 3 AR-Z 95/59 for Dr Mengele, Josef.
Known as the "Angel of Death", the Auschwitz doctor carried out horrific experiments on those held at the camp.
The record, prepared in the late 1950s, reads that his location is "presently unknown, likely in Argentina".
Mengele died in 1979 in Brazil, having evaded capture -- and justice -- for the remainder of his life.
However many more Nazis enter the dock or end up behind bars before all trails finally run cold, Rommel and his team know the overwhelming majority of perpetrators' stories will have ended similarly.
Nevertheless, he insisted, "we have to put every day to use if we want the chance to bring someone else to justice".