The defeat of Nazi Germany in 1945 brought with it the fall of a class of once powerful military commanders, government authorities and political henchmen who had formed the regime of Adolf Hitler.

Few U.S. intelligence officials came to know those men more intimately than did John E. Dolibois, who died May 2 in Wyoming, Ohio, at 95. His work as an interrogator was used in the war crimes trials at Nuremberg and provided insight into the psyches of the Nazi perpetrators.

Mr. Dolibois (who pronounced his name DOLL-ee-boy) came to the United States from his native Luxembourg as a boy and joined the U.S. Army during World War II. He served briefly in a tank unit before his superiors realized that he spoke fluent German and that they could more effectively employ him in military intelligence.

After witnessing the horrors at the Dachau concentration camp, he found himself in Luxembourg at a hotel-turned-jail in the town of Mondorf-les-Bains. The prison was dubbed the Ashcan and housed many of the highest-ranking Nazi officials awaiting trial at Nuremberg.

Among the detainees were Hermann Göring, commander of the Luftwaffe; Karl Dönitz, commander of the German Navy; field marshal Albert Kesselring; Albert Speer, the Nazi architect and minister of armaments and war production; foreign minister Joachim von Ribbentrop; and Julius Streicher, the fanatically anti-Semitic propagandist.

John E. Dolibois, who interrogated top Nazis after World War II and later became U.S. ambassador to Luxembourg, died May 2 at 95. (Family photo)

Mr. Dolibois once told the Washington Times that he began to understand the nature of his job when he reported for duty at the prison and was informed that “to get in here, you need a pass signed by God and then somebody has to verify the signature.”

Mr. Dolibois retired to his room and was putting away his things when he heard a knock. Expecting to find a fellow officer, he recalled in interviews, he opened the door and saw Göring, whose considerable girth made him immediately recognizable. Mr. Dolibois described the former commander as “about 5 feet 10 inches tall and 5 feet 10 inches wide and bedecked with medals.”

“I did a very poor representation of an intelligence officer,” Mr. Dolibois once told a Wisconsin newspaper reporter. “I stood there with my mouth open.”

Göring asked whether Mr. Dolibois was a welfare officer stationed at the prison to ensure that the Geneva Conventions were respected. Mr. Dolibois was in fact an interrogation officer, he said in an oral history with the U.S. Holocaust Memorial Museum, but he declined to correct the reichsmarschall’s misunderstanding.

That decision — along with his fluency in German — helped Mr. Dolibois establish an extraordinary level of trust with many of the prisoners in the months preceding, in many cases, their conviction and imprisonment or execution.

“He fit right in,” said Greg Peterson, a founder of the Robert H. Jackson Center in Jamestown, N.Y., which documents the history of the Nuremberg trials. “He didn’t assert himself. . . . He asked, he listened and he gathered as much information as anybody possibly could in that environment.”

Mr. Dolibois recalled that the Germans divided themselves into three camps — military brass, civil servants and party leaders — and that interrogators successfully used the divisions to their own advantage.

“The only pressure we ever used,” Mr. Dolibois once told CNN, “was, ‘Well, look, if you don’t want to cooperate for your own good, we’ll just send you over to the Soviet Union. They have ways of getting information. Would you rather go there?’ ”

In addition to his official work gathering intelligence,­­ Mr. Dolibois assisted with psychiatric evaluations. On numerous occasions, Mr. Dolibois helped administer Rorschach inkblot tests and translated the prisoners’ responses.

The tests produced revealing, sometimes disturbing results, said Eric Zillmer, a professor of psychology at Drexel University in Philadelphia and co-author of the book “The Quest for the Nazi Personality.”

Göring looked at an inkblot, laughed and said he saw two dancing figures clapping hands, according to Zillmer. Streicher identified a “flying dog from Borneo” and added that “it is also lifeless.”

By the end, Mr. Dolibois told the Cincinnati Enquirer, he had “seen enough prisons and prisoners.”

Jean Ernst Dolibois was born Dec. 4, 1918, in Bonnevoie, Luxembourg. His mother died shortly after his birth in the influenza epidemic.

With his father, a Frenchman, Mr. Dolibois came to the United States in 1931 and settled in Akron, Ohio, where a sister lived with her American husband. Mr. Dolibois was 12 at the time but said that he was placed in kindergarten because he did not speak English.

He later took the name John Ernest Dolibois and became a U.S. citizen. In 1942, he received a bachelor’s degree in psychology from Miami University in Oxford, Ohio.

Mr. Dolibois spent his postwar career at Miami University as an administrator and, among other endeavors, began a study-abroad program in Luxembourg. President Ronald Reagan nominated him in 1981 to be U.S. ambassador to Luxembourg, a post he held for four years.

His wife of 67 years, Winifred Englehart Dolibois, died in 2009. Their son Brian C. Dolibois died in 1991. Survivors include two sons, John M. Dolibois of Oconto Falls, Wis., and Robert J. Dolibois of Austin; four grandchildren; and eight great-grandchildren. John Dolibois confirmed his father’s death and said the cause was congestive heart failure.

After his retirement, Mr. Dolibois published a memoir, “Pattern of Circles.” He wrote that as a boy he visited Mondorf-les-Bains, where years later he would return as an interrogator. He had remembered the place, he wrote, “for its beautiful park, a quiet stream on which one could row a boat, lots of old trees and acres of flowers.”