COLUMBUS -- Growing up, Richard Makowski knew that his father had been imprisoned in a German concentration camp during World War II as an American citizen in Europe suspected of helping Poles resist the Nazis.

But he didn't dare ask for any details because his mother, Anne, warned it would give his dad terrible nightmares. And nobody -- least of all him -- wanted that.

As the years went by, Makowski intended to bring up the subject, but his father, Benedict Makowski, always seemed to be working.

Then the elder Makowski died in 1977 at age 60 from stomach cancer, ending any more chances to ask.

With Holocaust survivors getting older and dying, it's becoming harder for their loved ones to fill in the blanks of their family history.

Makowski, 64, of German Village, turned to the United States Holocaust Memorial Museum in Washington for help. Researchers there did everything possible to piece together what happened to his dad by scouring documents scooped up by Allied troops and put into a once secretive, but now public archive.

During the war, the Nazis kept meticulous records of their concentration and forced labor camps, as well as some ghettos. For more than 60 years, they were locked up in an archive in Bad Arolsen in central Germany. But in 2007, the International Tracing Service of the International Committee of the Red Cross, which administers the archive, began transferring digital copies of its documents to the Holocaust museum in Washington; Yad Vashem, Israel's Holocaust memorial; and the Institute of National Remembrance in Warsaw, Poland.

The collection contains more than 150 million pages of documents -- including arrival documents; death, prisoner and transportation lists; work-assignment records; and other information -- pertaining to 17 million people. Makowski's is one of more than 20,000 families the American museum has helped search for clues about their loved ones' experiences or fates.

"What is the greatest fear of survivors today? That when they are no longer here, what happened to them would be swept under the rug," said Paul Shapiro, head of the Washington museum's office of international affairs. "These millions of original documents are an insurance policy against forgetting."

It was fitting, Makowski said, to share what the museum discovered about his father in conjunction with International Holocaust Remembrance Day on Friday, which celebrated the liberation of the Auschwitz-Brikenau, the largest Nazi concentration camp, by the Soviet Army 72 years ago.

The primary objective of the remembrance was to honor both the deceased and surviving victims, as well as to promote awareness of the Holocaust, during which the Nazi regime killed millions of Jews and others in mass concentration camps across German-occupied Europe.

"It's like digging up the past to understand what they went through," Makowski said.

The fact that Makowski's father was an American citizen, born in Cleveland, was atypical, said Laura Ivanov, the museum's information retrieval specialist who handled Makowski's inquiry.

"We typically receive requests for people who were in Europe during the Holocaust who remained in Europe after the war's end," she said.

Also unique is the fact that Benedict Makowski was Catholic, she said. Poles were generally considered inferior by the Nazis, no matter what their religious affiliation, she explained.

Makowski said his grandparents, Feliks and Ludwika, separately came to the United States in the early 1900s. Both had relatives in Cleveland. They married in 1912 and had five children, three of whom survived: Alois, Joseph and baby Benedict. The family returned to Poland in 1921 and later had another child, a daughter.

Benedict Makowski was arrested by the Gestapo for an unknown reason in the city of Grudziadz in northern Poland on Oct. 15, 1943, according to documents located by Ivanov.

Makowski says the other members of his father's family had been picked up at various times, and his grandfather was killed en route to a camp.

Benedict Makowski was taken to the Stutthoff concentration camp, Ivanov said. Two months later, he was reportedly released and instructed to report for work detail in the town where he was arrested.

Makowski has been able to supplement the information provided by the museum with details provided by family members here and in Poland. He's traveled there twice. He's also done online genealogy searches.

Whatever the case, Makowski said, his father had to sign a certificate of release, saying he wasn't hurt or mistreated in any way and hadn't contracted any diseases, the documents show. "Can you even imagine?' he asked.

But his story has a happy ending.

He received a temporary U.S. passport and $20 loan from the state department that allowed him to return to Cleveland in August 1946, Makowski said.

That fall, he met the woman that he would marry at a family wedding. They married in February 1947.

"No one in my family knew or had anything like these documents," Makowski said. "I'm glad just to be able to share it with my siblings, and their sons and daughters and grandchildren."