Anthony Acevedo kept a wartime diary. (U.S. Holocaust Memorial Museum/U.S. Holocaust Memorial Museum)

During the winter of 1944-45, Anthony Acevedo was a 20-year-old Army medic assisting wounded soldiers fighting against Nazi forces in World War II. The war in Europe was coming to an end, but for Mr. Acevedo the horror was just beginning.

His ordeal in German prison and labor camps, which he kept hidden for decades, led to his recognition as the first Mexican American soldier to be designated a Holocaust survivor.

Mr. Acevedo was 93 when he died Feb. 11 at a veterans hospital in Loma Linda, Calif. He had congestive heart failure and chronic obstructive pulmonary disease, said a son, Fernando Acevedo. His death was first reported by CNN, which covered his funeral on March 8.

He was a corporal when he and other members of his depleted unit were captured Jan. 6, 1945. He was first taken to a large POW camp, Stalag IX-B, where he was interrogated by a German officer.

“He pointed at me with his baton,” Mr. Acevedo told the Press Enterprise of Riverside, Calif., in 2009. “He knew everything about me. He knew about my family. He talked to me in Spanish and English. He said, ‘You were born in San Bernardino and raised in Pasadena. Your parents were kicked out of the United States. That’s what the Americans do.’ ”

All the facts were correct: Mr. Acevedo’s Mexican-born father was an engineer who worked on U.S. government projects before his family was deported in 1937 for not having proper immigration papers.

Anthony Acevedo’s World War II armband as an Army medic. (U.S. Holocaust Memorial Museum/U.S. Holocaust Memorial Museum)

Anthony Acevedo was 13 at the time. While living in Durango, Mexico, he and a friend deciphered Morse code messages sent by two German men to submarines off the coast and turned them in to the police. The Germans were prosecuted for espionage.

Mr. Acevedo’s interrogators at the POW camp knew all these things and believed Mr. Acevedo was withholding other information and was possibly a spy.

“I kept saying, ‘I don’t know nothing,’ ” he later recalled. “They slapped my face and put needles under my fingernails.”

During a roll call in early February 1945, the Germans ordered all Jewish prisoners at Stalag IX-B to step forward, then selected others who “looked” Jewish, were seen as troublemakers or were deemed “undesirable.” Mr. Acevedo, who was Catholic, was one of 350 men told they were being sent to a “beautiful camp” with a theater and entertainment.

“It turned out to be the opposite,” he told CNN in 2008. “They put us on a train, and we traveled six days and six nights. . . . They had us 80 to a boxcar. You couldn’t squat.”

The train stopped at Berga an der Elster, a subcamp of Buchenwald, one of Germany’s largest concentration camps. It was a slave labor camp, where U.S. service members and other prisoners were forced to dig tunnels for the Nazi war effort.

As a medic, Mr. Acevedo cared for his fellow prisoners and was exempt from hard labor. But he still endured harsh treatment, including beatings and other forms of brutality.

The prisoners received occasional packages of food from the Red Cross, but they subsisted largely on bread made from sawdust, ground glass and barley. They sometimes thickened their soup with the flesh of rats or stray cats they managed to capture. At night, they had to sleep two to a bunk, naked and without blankets.

Many prisoners had diarrhea, and they soon began to die from dysentery and malnutrition. Others who attempted to escape or who faltered in their work were shot in the forehead. After witnessing their murders, Mr. Acevedo had to plug the fatal wounds with wax.

After arriving at Berga, Mr. Acevedo began keeping a secret diary, labeled “A Wartime Log.” Writing with a fountain pen, whose ink supply he extended with snow and urine, he chronicled the experience he and his fellow prisoners faced:

April 2, 1945

Two more of our men died today + one last night makes 3 + 16 — makes 19; living in unsanitary conditions; water must be boiled before it is drinkened. No latrines. Deaths are increasing in great number.

Mr. Acevedo recorded the name of every prisoner who died, the date and cause of death.

“Prisoners were being murdered and tortured by the Nazis,” he told CNN. “Many of our men died, and I tried keeping track of who they were and how they died. I’m glad I did it.”

Throughout the diary, Mr. Acevedo reported snippets of news, including the death of President Franklin D. Roosevelt, which he noted on April 13: “We held a prayer service for the repose of his soul.”

Then: “Burdeski died today.”

As Allied troops began to close in, the Germans decided to evacuate the Berga camp. On April 6, Mr. Acevedo and his fellow prisoners began a forced march to parts unknown.

He and other medics pushed a two-wheeled wooden cart, stacked with as many as 20 bodies of men too sick to walk or already dead. Some were buried along the side of the road.

After more than two weeks, Mr. Acevedo and the other prisoners could hear the sound of guns in the distance. At last, U.S. soldiers reached the barn where they were resting, and the German guards took flight.

“We were liberated today,” Mr. Acevedo wrote, “April the 23/1945.”

He and his fellow prisoners had walked 217 miles in 17 days.

Of the 350 U.S. soldiers shipped to Berga in February, only 120 survived. Mr. Acevedo, who was 5-feet-10, weighed 149 pounds when he was captured in January. In 3½ months, he was down to 87 pounds.

Army officials required Mr. Acevedo and the other survivors to sign an affidavit, pledging not to say anything about what they had witnessed.

“You must be particularly on your guard with persons representing the press,” the document noted. “You must give no account of your experience in books, newspapers, periodicals, or in broadcasts or in lectures.”

Years later, the Army explained that it was an order of short duration, meant to keep military maneuvers secret. But Mr. Acevedo and other prisoners interpreted it as a lifetime oath of silence.

If he tried to tell others, Mr. Acevedo said in 2009, “No one would believe it. People would say, ‘Oh come on, you’re just making a story out of it.’ ”

Anthony Claude Acevedo was born July 31, 1924, in San Bernardino, Calif. He attended segregated schools in Pasadena with black, Asian and Hispanic students.

Mr. Acevedo spent his teen years in Mexico before crossing the border to enlist in the U.S. Army. After the war, he was reunited with his family in Mexico.

“My father asked me why I surrendered,” he told the Press Enterprise. “In other words, he was saying I was a coward. I didn’t see him for seven years after that.”

Mr. Acevedo later worked as a surgical technician, then became a design engineer for aerospace companies in Southern California. He retired in 1987.

He spent more than 20 years as a volunteer at the veterans’ hospital in Loma Linda, where he died.

His first marriage, to Amparo Martinez, ended in divorce. His second wife, Dolores Maria Lamb, died in 2014 after more than 20 years of marriage.

Survivors include four children from his first marriage, Tony Acevedo of Westminster, Calif., Rebeca Acevedo-Carlin of Cerritos, Calif., Fernando Acevedo of Rancho Cucamonga, Calif., and Ernesto Acevedo of Lake Elsinore, Calif.; two brothers; a sister; and six grandchildren.

Mr. Acevedo first spoke publicly of his wartime experiences to CNN in 2008. The Army later determined that he and other prisoners from Berga were not ordinary POWs but were victims of Germany’s network of concentration and slave labor camps.

In 2010, the U.S. Holocaust Memorial Museum in Washington acquired Mr. Acevedo’s diary and other artifacts and interviewed him for an oral history. He became the first non-Jewish Mexican American to be recognized as a Holocaust survivor.

“Tony’s was the first diary the museum received that was written by an American in a concentration camp,” Holocaust Museum curator Kyra Schuster said in an interview. “When Tony donated his collection, other Berga families came forward. Every time I tell their story, the reaction I get is, ‘I never heard this before.’ If Tony hadn’t spoken up, we would never have had their story.”

A final revelation in Mr. Acevedo’s saga came in December 2017, when his son Fernando discovered a 1996 psychological interview conducted for a military disability application. In it, Mr. Acevedo revealed that his treatment was worse than he had ever admitted: In the labor camp, his German captors subjected him to a savage gang rape.

His son asked if it was true.

“Oh, yeah,” Mr. Acevedo said. “I want you to tell everybody. I want you to tell everybody what I went through.”