BERLIN (AP) _ Robert M.W. Kempner, a German-born member of the U.S. prosecution team at the Nuremberg war crimes trial and a leading author on the Holocaust and the Nazi era, has died at age 93.

Kempner had been in ill health for months, although he continued to work on his legal practice whenever possible. He died Sunday in Frankfurt, his office announced Monday. No cause of death was given.

An early opponent of the Nazis, Kempner had to emigrate after Adolf Hitler's rise to power. Eventually taking up residence in the United States, he later became a professor at the University of Pennsylvania.

Kempner had been chief legal adviser to the police in Prussia, then the largest German state. When he joined the prosecution team at Nuremberg, his knowledge of police administration helped the Allies understand how the Nazis worked, according to the 1992 book ''The Anatomy of the Nuremberg Trials'' by Telford Taylor.

Among Kempner's coups was the discovery of the so-called Wannsee Protocol, the record of the meeting in 1942 at which top Nazi officials approved plans for the ''final solution of the Jewish problem'' - the murder of six million European Jews.

Kempner found the document in 1947 in Foreign Ministry archives in Bonn while researching for the post-Nuremberg trial of ministry officials.

Kempner was fired in 1933 by Hermann Goering after the Nazis took power. Thirteen years later, he was chief of the division preparing the case against Goering and other defendants in the main Nuremberg war crimes trial.

At one point he reluctantly tried to persuade Goering to testify against his co-defendants.

Goering was willing only if he were to be given an honorable death by firing squad rather than be hanged, and the effort came to nothing, according to the book ''The Nuremberg Trial'' by Ann and John Tusa.

Kempner, the Tusas wrote, ''felt that no one should deal with such a man; no one should sup with such a devil however long their spoon.''

Goering took poison. Ten other top Nazis were hanged.

The Tusas' book portrays Kempner as a keen observer of German public opinion during the war crimes trials. He was concerned that many Germans thought the main trial was only an Allied propaganda exercise, and worked to get Germans into the sessions to see the even-handed procedures.

Kempner had tried in 1931 to drag Hitler before the courts on charges of treason and perjury, to have the National Socialist Party declared illegal, and to expel the Austrian citizen Hitler as an ''undesirable alien.'' After the Nazis' came to power, Kempner spent time under Gestapo arrest before fleeing Germany.

He established a law practice in Frankfurt in 1951 and wrote many books and articles while working as a prosecutor in trials for the murder of Anne Frank and war crimes in the Warsaw Ghetto.

He was an expert witness at Israel's 1960 trial of Adolf Eichmann, one of the participants in the ''final solution'' meeting.

Kempner's memoirs were published in 1983 with the title ''Accuser of an Epoch.''

His wife, Benedikta Maria, died 10 years ago. Survivors include two sons, Lucian and Andre, four grandchildren and two great-grandchildren.

Kempner is to be buried Aug. 24 in Berlin.