(CNN) -- A jury's decision in July to acquit George Zimmerman in the murder of Trayvon Martin represented "questionable judgment," former Secretary of State Colin Powell said in an interview aired Sunday.

But the retired four-star general, who was the first African-American to serve in the top U.S. diplomatic post, went on to suggest the case wouldn't have a lasting impact on Americans' lives.

"I don't know if it will have staying power," he said on CBS's "Face the Nation."

"These cases come along, and they blaze across the midnight sky and then after a period of time, they're forgotten," he said.

Zimmerman, a neighborhood watch volunteer who fatally shot Martin in February 2012, was acquitted by a jury in July on state criminal charges. The case sparked a nationwide discussion of race. Martin was an unarmed black teenager, and Zimmerman identifies himself as Hispanic.

After the verdict, President Barack Obama delivered a personal statement about the case, delving deeply into issues of race and justice, and connecting the difficulties facing American-American men to situations he himself had faced.

Powell said Sunday he'd like Obama to "be more passionate about race questions."

"In my lifetime, over a long career in public life, you know, I've been refused access to restaurants where I couldn't eat, even though I just came back from Vietnam. 'We can't give you a hamburger, come back some other time,'" Powell said, adding that while progress has been made toward racial equality, there is still work to be done.

"We're not there yet," he said. "And so we've got to keep working on it. And for the president to speak out on it is appropriate. I think all leaders, black and white, should speak out on this issue."

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