As a 20-year-old U.S. Army soldier in the all-black 183d Combat Engineers Battalion, Leon Bass arrived at the Nazis' Buchenwald extermination camp just one day after it had been liberated in April 1945.

Bass saw the living skeletons of those who survived. The camp reeked of burned human flesh. The torture chambers were still covered in blood.

After the war, Bass left the Army as a sergeant, returned to Philadelphia, and eventually became principal of Benjamin Franklin High School. He earned a doctorate in education from Temple University.

He somehow put the horrors of Buchenwald behind him for 23 years.

But in 1968, a woman who survived the Holocaust spoke to his Benjamin Franklin students, who were less than attentive. Suddenly, Bass ordered the students to listen, telling them he also had seen the horrors the woman was describing.

Afterward, the woman thanked him, and later he received a request to speak publicly about what he had seen as a liberator.

Mr. Bass, 90, who died Saturday at Pennswood Village in Newtown, Pa., where he had lived for 17 years, continued to speak out decade after decade, regularly appearing at Holocaust remembrance events honoring survivors and liberators.

"The last time he spoke was in October in Washington," said his daughter, Delia Bass-Dandridge. "He was pretty remarkable."

Robbie Waisman, 83, a Holocaust survivor who lives in British Columbia, told the Vancouver Province newspaper in January he had never seen a black man until Mr. Bass and members of his segregated unit arrived at Buchenwald.

"I remember thinking it must not be happening. I went to touch one of them to see if they were real. They were," Waisman told the newspaper.

Waisman and Mr. Bass repeatedly spoke together to Canadian and U.S. audiences about experiences during the war.

Mr. Bass explained that racism and anti-Semitism were manifestations of human hatred that constantly must be fought.

Mr. Bass recalled that after he told students about his experiences, one of them asked why he had not spoken out before 1968 about the horrors of the war.

He said it was one of the hardest questions he'd ever been asked. He told the student he had made a huge mistake. Although he correctly was attending to work and his family, he said he neglected a huge duty he had to tell everyone who would listen about what he had seen.

Mr. Bass received numerous human rights commendations, including the Pearlman Award for Humanitarian Advancement from Jewish Women International.

Mr. Bass, who authored the book Good Enough: One Man's Memoir on the Price of the Dream, was featured in the documentary film Liberators: Fighting on Two Fronts in World War II.

In addition to his daughter, Mr. Bass is survived by his son, Leon Jr.; four grandchildren; and one great-grandchild.

There will be a private service for the family, and a memorial service is to be announced.