Kenneth Walker, an Emmy Award-winning journalist whose reporting for the ABC News program “Nightline” helped bring the brutality of South Africa’s racist apartheid system to the attention of the American public, propelling it onto the agenda of U.S. policymakers, died on April 11 in Washington. He was 73.

His cousin and executor, Jeff Brown, said his death, in a hospital, was caused by a heart attack, It was not widely reported at the time.

Mr. Walker’s weeklong coverage of South Africa’s often brutal policy of racial segregation — produced for “Nightline” with Ted Koppel, the program’s anchor, and a team of reporters — won a 1985 Emmy Award from the National Academy of Television Arts and Sciences for outstanding analysis of a news story. It was also awarded an Alfred I. duPont-Columbia Gold Baton.

“In the way that only television can, ‘Nightline’ revealed for viewers the pain, anguish and rage that suffuses the struggles of this divided country,” the duPont-Columbia citation said. “Masterfully executed and exquisitely produced, it was perhaps the most powerful, certainly the most extraordinary, television of the year.”

The National Association of Black Journalists named Mr. Walker journalist of the year in 1985 for that reporting. The association had already given him an award for his work in print journalism — for his four-part series on apartheid for The Washington Star — and when he won the association’s top award for radio journalism in 2001, he became the first person to receive its highest honors for print, television and radio.

The association later honored him further, with its Frederick Douglass Lifetime Achievement Award.

During his four-decade career, Mr. Walker was a reporter for The Washington Star (from 1969 to 1981, when it folded), for “Nightline” (from 1981 to 1988) and for NPR, where he served as Africa bureau chief from 1999 to 2002.