That his work was not lost is thanks to chance and the quick work of a handful of local investigators and a retired mailman, who chased an odd trail that involved a former legal secretary and a Canadian professor with an interest in historical documents.
For Kempner's work to have vanished would have been devastating, say experts.
"That kind of information will never appear anywhere in the official record," said Henry Mayer, chief archivist at the U.S. Holocaust Museum in Washington. "If it were lost, you really wouldn't know what happened."
Until his death six years ago at 93, Kempner, a German-born lawyer, dedicated his life to fighting on behalf of victims of the Holocaust.
He spent his early years studying law in Germany, where he became a legal adviser to the Prussian state police before Adolf Hitler came to power. He was an early and outspoken opponent of the Nazis.
Although he spent time under arrest by the Gestapo, he continued to advise Jews emigrating to escape the Nazis until he himself fled to the United States in 1939, where he became a professor at the University of Pennsylvania and eventually settled with his family in Lansdowne.
After the war, he returned to Germany and took a place as a lead prosecutor on the U.S. team of lawyers at the Nuremberg military tribunal, where his knowledge of police administration from his prior post helped shed light on the workings of the Nazis.
Kempner is also credited with discovering in German archives in 1947 what is now known as the Wannsee Protocol, the record of a 1942 conference at which high-level Nazis approved "the final solution," a blueprint for the murder of six million Jews.
He continued his work in his private legal practice from his residences in both Delaware County and Frankfurt, and specialized in restitution claims filed by victims of the Nazi era.
He also collaborated long after the war with others to chase down Nazis who remained unpunished.
Those who knew him remember Kempner as single-minded in his pursuit of what he explained to a reporter during one of his last interviews as his desire to "put a little piece of justice back into the world."
"He was a man who didn't like to be disturbed," remembered Magnus O'Donnell, a retired Upper Darby postal worker who befriended Kempner and his wife, Benedikta Maria, in the 1960s when their house on a leafy, tucked-away section of Lansdowne Court was on his route.
Mail was often of vital importance to Kempner's work, explained O'Donnell, now 72, who later became the caretaker of the Lansdowne house and a trusted family friend. Even after Kempner's death in 1993 - and after the home's last resident, Kempner's former legal secretary, Margot Lipton, left for a nursing home last year - he continued to look after the property.
So it was O'Donnell who first became concerned when Kempner's carefully stored papers and books were hauled off in boxes in late 1998.
O'Donnell said he watched as the papers were removed. "I was concerned - but what could I do?" he said.
An unrelated property dispute between Lipton and Kempner's son, Lucian, brought the missing documents to light.
In his will, written on a sheet of paper, Kempner left his possessions to his two sons - Lucian, who resides in Germany, and Andre, who has died. Kempner made one exception in his will for his trusted secretary, Lipton, who he stated would be allowed to live in his house with all its possessions until her death.
Lipton, who is in her 80s, was called to testify in a deposition this summer, and at that time agreed that the contents of the Lansdowne house should be transferred to the U.S. Holocaust Museum, to which his sons had donated his estate, according to Kevin Gibson, a Media lawyer representing Lucian Kempner.
But when Gibson and museum officials arrived at the Lansdowne house, they found it empty.
"It was obvious that someone had taken Dr. Kempner's things - there were packing crates and bubble wrap strewn all about the house," said Gibson, who promptly called the police.
With the help of O'Donnell, investigators followed the trail of the missing documents, and the mystery began to unravel: Lipton had become acquainted with a former religious-studies professor named Herbert Richardson, who persuaded Lipton to sign over legal decision-making power to him and move to an assisted-living facility in Lewiston, N.Y., near where he lived, detectives said. He then persuaded her to move Kempner's estate in November 1998, detectives said.
Lipton is no longer of sound mind, according to Delaware County District Attorney Patrick L. Meehan.
Lewiston is the home of the Edwin Mellen Press, an academic publishing company in which Richardson has a business interest. In 1994, he was fired from his post at the University of Toronto for, among other things, failing to disclose that involvement.
"We find out this Richardson fellow had inserted himself into Margot's life and within a few months she's moved to upstate New York and all these items are taken with them," said Sgt. Joseph Ryan, a detective in Delaware County. "It was pretty suspicious."
Authorities recently tracked the documents to a white clapboard two-story house in Lewiston, which bore a neat wooden sign on its front lawn that advertised "The Robert Kempner Collegium." But the building apparently was not open to the public.
When detectives met with Richardson in New York, the former professor agreed to relinquish the documents to the Holocaust Museum, Meehan said.
Ryan said Richardson told the detectives that "he was trying to help them . . . and make sure the Kempner collection was preserved," said Ryan.
No charges were filed, but Ryan said Richardson's dealings with Lipton are still being investigated. Over the last week, Richardson has not responded to several messages. He was out of the country and unavailable for comment yesterday, a receptionist at the Edwin Mellen Press said.
Earlier this month, the materials were moved to the Washington museum. Officials there will spend some time sifting through the collection, which consists of about 500 cubic feet of material.
In it are items such as letters between Kempner and clients from Holocaust reparations cases and his personal notes from the Nuremberg trials.
Both, said Mayer, lend valuable historial insights into the personalities of the Nazi era, what happened to victims, and legal strategies used at the trials that provide important precedents for war-crimes trials of the future.
"The more we study the Nuremberg trials, the more we know how to proceed today," said Mayer. "It's what we can learn from the past, and how we can do it better."
Or as Kempner himself once put it, "The world must do something, so it doesn't happen yet again."