BERLIN — Who's the culprit? At first sight, the question seems simple enough to answer. Obviously, the guilty party is the one who commits a crime, "with his own hands," we might add. But this definition is of course not always enough, especially when it comes to complex criminal networks. Heinrich Himmler for instance, probably never killed anybody "with his own hands," and yet he was one of the Holocaust's main criminals. Just like Adolf Eichmann, the man who organized the mass deportations of Jews to concentration camps.

And what about for lower-ranking accomplices? The conductors who drove the trains to the concentration camps? The guards who prevented people from escaping when they were on their way to the gas chambers? The ordinary people who did nothing to stop the mass killings?

Current penal law in Germany calls it "aiding and abetting" of murder. Recently prosecutors opened new homicide cases against former concentration camp staff. None of the eight suspects, all now between 88 and 98 years old, are accused of carrying out a single murder, but rather of contributing to systematic killing.

Since there is no statute of limitations on murder, criminal proceedings can begin even 70 years later. Since 2011, 58 cases have been opened against people accused of being part of the staff of such extermination camps as Auschwitz-Birkenau or Majdanek. Fifty-two of the proceedings have been closed, while two have led to convictions and four cases still underway.

If there are still that many potential culprits alive after seven decades, the question arises: How many culprits were there in total? It is a question that goes well beyond the workings of a criminal justice system.

Frank Bajohr of Munich's institute for contemporary history, has delved back into the issue, which was first a topic for study in the 1990s. Today, we think that there have been 200,000 to 250,000 German, Austrian and "ethnic German" Holocaust culprits. To this must be added a not easily quantifiable number of collaborators from Lithuania, Latvia and Ukraine who committed pogroms against Jews or acted in some other way as "volunteers" to aid the carrying out of the killings.

If you take a closer look at the German culprits, one notices that as a matter of fact, a disturbing number of them can be qualified either as sadists, or otherwise mentally ill. But the majority was quite sane. Another theory that Bajohr refutes is the assumption that the cruelties experienced during World War I could be held responsible for the crazy killing during World War II.

Individual motives like greed, jealousy, sexual motives and other typical triggers — something criminologists instinctively always look for first — could not be found with the majority of culprits either.

Something that has clearly been disproved is the common allegation that Nazi culprits acted under superior orders, fearing for their own life if they didn't obey. It's actually quite the opposite: Often it was the free choice to sign up to participate in the mass killing.

So what was it that made ordinary people, Germans and Austrians, kill thousands of defenseless people, sometimes in acts of direct violence, often in less direct ways?

The murder factories of Auschwitz-Birkenau, Belzec, Sobibor and Treblinka where a few offenders killed enormous numbers of humans with the help of technical support, were responsible for "only" half of the six million victims of the Holocaust. The rest were hunted down, shot or starved to death before the eyes of many. What explains the ease of this immense outbreak of violence?

Comradeship plays a major role, without a doubt. Bajohr describes it with the help of a 1933 quote from the publicist Sebastian Haffner that relates to a training camp for lawyers-to-be: "Comradeship entirely eliminates the feeling of individual responsibility. The person simply behaves like everybody else, does what everyone does."

That's how many but not all of the Holocaust crimes can be explained. With its open anti-Semitic politics, the Nazi regime outlawed the very existence of Jews. Most people's individual conscience had been turned off. They knew that they were part of the machinery of destruction, even those who were typing letters in the concentration camps' offices. But, a perverse reinterpretation of the word "comradeship" made them consider it their duty to continue, to "function."

Most culprits have, more or less, gotten away with their crimes. In total, only about 7,000 have been convicted in German courts, 172 with life imprisonment. It is a frustrating result, considering the 170,000 accused by authorities. Some 30,000 to 80,000 of the missing ones, did not live past the year 1945, but the majority simply went underground, managing to avoid public prosecution. And thus we are with the lessons of history, which include this dictum: Without an accused, there is no trial.