By Mario Cacciottolo
Serge Klarsfeld does not look like someone who would put a gun to a man's head.
This avuncular 73-year-old is the epitome of politeness in his large office, with a photocopier whirring in the corner, brightly coloured document folders stuffed in many shelves, and cats tiptoeing over papers and desks.
But once, in 1973, Mr Klarsfeld, brandished a pistol in the street at a former World War II Nazi - Kurt Lischka, wartime Gestapo chief for Jewish affairs in France, who was living comfortably in Cologne.
This was just one of many dramatic moments in the life of Mr Klarsfeld and his wife Beate, who have carried out a battle over almost 40 years to seek justice for the Nazis' victims in France.
This battle is now over, because either all those linked to the crimes are dead, or, the Klarsfelds say, there is not enough evidence to prove their guilt in court.
Mr and Mrs Klarsfeld had already failed in a previous attempt to kidnap Lischka, who was instrumental in planning the deportation and subsequent murder of thousands of French Jews and other "enemies" of the Third Reich.
Mr Klarsfeld's ploy with the gun was designed to persuade the West German government, which had been refusing all calls to prosecute Lischka, to think again.
"I went to Cologne and approached Lischka in the street. I put a gun to his forehead - he had a gun himself, but he just threw up his hands. The eyes of a man are terrible when he thinks he's going to die.
PURSUED BY THE KLARSFELDS
Responsible for deportations to concentration camps, jailed for 10 years
'Butcher of Lyon', sentenced to life imprisonment for crimes against humanity
Sentenced to 10 years in jail for helping send more than 1,600 French Jews to die in concentration camps
Former aide to Klaus Barbie, executed seven Jews, convicted of crimes against humanity and jailed for life
Sent tens of thousands of Jews to their deaths, convicted in absentia in 2001 and sentenced to life imprisonment, last seen in Syria and considered likely to be dead
"I didn't shoot, and escaped, and then wrote to the West German government to say that if they did not deal with this man, then we could. We told them to do their duty and apply the law."
That did not happen right away, and instead a warrant was issued for both the Klarsfelds' arrest. But Lischka was eventually tried and convicted, in Cologne in 1980, receiving a 10-year prison sentence.
Mr Klarsfeld's wife Beate, 70, explains there were not actually any bullets in her husband's revolver.
The daughter of a German soldier, she left Germany in 1960 and married Serge in Paris in 1963, becoming a famed pursuer of Nazis in her own right.
Confronting the past
The couple's comfortable offices, in Paris's eighth arrondissement, are covered with documents and books on the Holocaust - they are piled on chairs, tables and floors.
Mr Klarsfeld explains that they began to realise in the 1960s that former Nazis were leading respectable lives in German society, as judges, politicians and businessmen. "This was something that we could not stand," he said.
Beate and Serge Klarsfeld have dedicated their lives to pursuing Nazis
And so the couple dedicated their lives to the pursuit and the prosecution of former Nazis, by what they describe as both "legal and illegal" measures, forcing French people to confront the truth of their compatriots' widespread complicity in Nazi crimes.
Mrs Klarsfeld said the couple were not Nazi hunters, "because we didn't have to hunt them, we knew where they were, living openly". A lack of political will meant prosecutions of Nazis had dried up.
"In France we changed the memory of the Vichy government, showed up the crimes of the Vichy, like deporting children from France," he said.
"We did it by providing information and research on how the Vichy co-operated with the Nazis. We were involved in the prosecutions of collaborators like Maurice Papon and Paul Touvier.
"The French population forgot what had happened. In 1970 the French public thought those who were arrested in our country were arrested by the Germans, but we showed that most often it was by those in French uniforms."
Most famously, Mrs Klarsfeld, a German from a Christian background, publicly slapped the West German Chancellor Kurt-George Kiesinger in 1968, because of his former role as director of Nazi propaganda broadcasting, a blow that resonated around Europe and that helped bring about Kiesinger's fall from power.
That slap is still discussed in German schools today, such was its significance.
Mrs Klarsfeld in particular has carried out protests over former Nazis and anti-Semitism in countries such as the former West Germany, Poland, Czechoslovakia, Chile and Syria, mostly leading to arrests and frequently deportation.
"I knew I had to go wherever the people were suffering," Mrs Klarsfeld said. "Sure, it could be dangerous. But if you really want to do something with your life, you have to do more than just speak."
The couple also tracked down the infamous Nazi Klaus Barbie, member of the Gestapo and known as the Butcher of Lyon. There is evidence Barbie personally tortured prisoners and was blamed for 4,000 deaths and a further 7,500 deportations during the war.
The Klarsfelds found Barbie in Bolivia and helped organise his extradition in 1983, after first conspiring to kidnap him. Mr Klarsfeld legally represented more than 120 of Barbie's torture victims.
Barbie was sentenced to life imprisonment for crimes against humanity in 1987, and died in prison in 1991. On his first court appearance he said: "All my troubles in the past started when Madame Klarsfeld came to Bolivia."
The Klarsfelds stopped looking for Nazis themselves after a trial in absentia of Alois Brunner in 2001 in Paris, which they had pressed for and in which they presented evidence. Brunner was sentenced to life imprisonment.
Brunner is the former head of an Austrian SS anti-Jewish team, and the man whose orders led to Mr Klarsfeld's father being gassed in Auschwitz in 1943.
Although Brunner could still be alive - he was once sighted in Syria - he would be almost 97 and both the Klarsfelds believe that he is long dead.
"He was ill and had been sent two letter bombs, which blinded him in one eye and took off most of his fingers on one hand - he undoubtedly died a long time ago," Mr Klarsfeld said.
Nor do the Klarsfelds expect to be dealing with any further cases of Nazi war criminals.
"You have to have documentary evidence that you can use in court, and there no longer is any such evidence available on anyone still alive, in France at least," Mr Klarsfeld said.
'People like us'
He says he always kept an emotional distance from the people he was pursuing. He didn't hate them.
"After all, they were people like us. We spoke with some of them. They like animals, we like animals, for example.
"But we never met anyone who had changed, never met a former Nazi who showed remorse. They were only interested in their own situation and that of their family.
The Klarsfelds tracked Klaus Barbie down to Bolivia
"I never felt frustrated if a Nazi died before we could bring him to trial. I cannot wish these people a long life."
Mrs Klarsfeld, however, takes a different view.
"You can hate them. If you look at the documents, look at what they've done, and how they've never show remorse. Awful, awful."
These days the Klarsfelds are busy with many projects - Mr Klarsfeld runs an organisation called the Sons and Daughters of Jews Deported from France, and has published several volumes of a book which catalogues the names, ages and addresses of French children deported in the war.
As a result of their efforts, the Klarsfelds themselves have been arrested, deported, beaten, had two attempts made on their lives and even been put on trial, but they have also been showered with international honours.
Among many other awards, both were given the Legion of Honour by France in 1984. Mr Klarsfeld has also been awarded full Israeli citizenship.
"Having left Germany when I was young, I couldn't have dreamed one day to be what I am today," Mrs Klarsfeld said.
"We tried to do quite a lot. We acted very often illegally, but our illegality is nothing compared with the people we had in front of us."