The question was put by Professor Michael Bazyler, a leading Holocaust scholar, to Rabbi Harold Schulweis, founder of Jewish World Watch, a Jewish organization committed to living out the moral imperative of never again.
Here is the exchange between Bazyler and Schulweis:
Professor Bazyler: “… I want to take the prerogative before getting the audience to ask questions to ask a question of Rabbi Shulweis that always comes up when I talk to students. It’s based upon a statement that Yehuda Bauer, the Holocaust historian at Yad Vashem makes and he says that says you know we the Jews, the people of the Book, we’ve been given the 10 commandments and he would add an 11th commandment: “Thou shalt not be a bystander.” In talking to the various people that are the righteous, that are the rescuers, is there a common trait, is there something in them that you find that made those people, not bystanders but rescuers?
Rabbi Schulweis: Years ago we started an organization called the Foundation for the Investigation of the Altruistic Personality. One of them was a good friend of mine called Perry London who would get a lot of interviews and I must say towards the end he came up with nothing. That is what I think is the mystery of goodness…. I keep asking that question. Perry London suggested a certain kind of adventurous personality, a certain kind of initiative, but I didn’t find that to be the case, neither did he. He found people who were very ordinary very passive, suddenly there is something that happens, I don’t know. Do you know who is gonna save you? Can you guess right now? I’m sorry to disappoint you.
Well it did disappoint me. There is nothing unique in the personality of a rescuer that distinguishes him or her from the rest of the crowd? I did a little more research and came upon numerous references to the Perry London study that Rabbi Schulweis mentioned. Here is how one author, John Conroy, summarized Perry London’s research on Holocaust rescuers:
One small study of people who helped Jews during the Holocaust, described by Perry London in “The Rescuers: Motivational Hypotheses about Christians Who Saved Jews from the Nazis” … found evidence to indicate that altruistic behavior was related to three personal traits:  a spirit of adventurousness,  an intense identification with a parent who set a high standard of moral conduct, and  a sense of being socially marginal. In London’s small sample, the spirit of adventurousness was perhaps best exemplified by a man whose prewar hobby was to race motorcycles on courses that required driving over narrow boards that spanned deep ditches. Once the war began, that man and his friends got a kick out of putting sugar in the gas tanks of German army vehicles, a practice that disabled the engines. The identification with a parent with high moral standards was prominent in the case of a Seventh-Day Adventist minister from the Netherlands whose father had gone to jail for his beliefs; the minister described himself as mildly anti-Semitic, but during the war he organized a large-scale operation for rescuing Jews, believing simply that it was a Christian’s duty. That minister, who belonged to a religious group with an extremely small number of followers in Holland, was also cited as an example of what the researchers called “social marginality”: a social separateness, a feeling of being an outsider, that seemed to allow the rescuers to have less fear about losing their attachment to the majority group. One highly effective German rescuer, also part of London’s sample, had been a stutterer as a child and in an interview confessed that he had always felt friendless. The residents of the French village of Le Chambon, who saved thousands of Jews during the war, also had a certain social marginality: they were Huguenots in overwhelmingly Catholic France.
That seems to make more sense to me. You could almost summarize these personality traits as (1) courage; (2) moral conviction; and (3) social marginality. For me at least, it is unsatisfying to say that there is nothing unique about a rescuer. But it also makes sense to say that it’s not religion per se that defines a rescuer, for religious people are perpetrators, bystanders, and rescuers. So perhaps what distinguishes the average person who is a bystander from the exceptional person who is a rescuer is that the latter has courage, conviction, and detachment. Or perhaps Rabbi Schulweis is right. Perhaps there is nothing unique about a rescuer, except that he is utterly ordinary and happens to perform extraordinary deeds.