7:32 p.m. EST March 6, 2015 President Obama said Friday that the federal investigation of Ferguson, Mo., revealed a police department "systematically biased against African Americans in that city."

But he also said he doesn't believe Ferguson is typical of most police departments.

"The overwhelming number of law enforcement officers have a really hard, dangerous job and they do it well, and they do it fairly, and they do it heroically. I really believe that," Obama said at a South Carolina college.

Obama's comments on Ferguson were his most extensive since the Justice Department released its report on the August shooting of Michael Brown, an 18-year-old black man shot by a white Ferguson police officer.

Attorney General Eric Holder, traveling with the president, told reporters that he's prepared to seeking the dismantling the Ferguson Police Department if necessary to change the culture of policing in the St. Louis suburb,

"We are prepared to use all the powers that we have, all the power that we have, to ensure that the situation changes there," he said. "That means everything from working with them to coming up with an entirely new structure."

In the report released Wednesday, federal prosecutors said there wasn't enough evidence to charge Officer Darren Wilson with a federal crime. But the investigation uncovered disproportionate arrests of minorities and a practice of using criminal fines to raise money for the city's coffers, which Holder called "appalling."

"It was available for everyone to read," Obama said. "What we saw was the Ferguson Police Department, in conjunction with the municipality, saw traffic stops, arrests, tickets as a revenue generator as opposed to serving the community."

Federal investigators also found racist e-mails by city officials. Two Ferguson police officers, Rick Henke and William Mudd resigned Thursday after they were suspended over racist emails, according to the Ferguson city attorney. A third person, Mary Twitty, a court clerk, was fired on Wednesday.

Obama focused on criminal justice and civil rights during his appearance at Benedict College, a 145-year-old historically black college in Columbia, S.C. The town-hall-style event was billed as a preview to Obama's speech in Selma, Ala., on Saturday for the 50th anniversary of the voting rights march known as "Bloody Sunday."

"One of the things I might talk about -- I'm still working on my speech, but it might come up, is the meaning of Selma for your generation," Obama said. "Selma is now, Selma is about the courage of ordinary people doing extraordinary things, because they believe they can change history."

Obama also addressed broader issues in the criminal justice system — issues that go all the way to the Oval Office. Obama said he has the constitutional power to shorten sentences and grant pardons.

He said when he first took office, "I wasn't really getting a lot of recommendations for pardons, at least not as many as I would expect," he said. And those he did get were from "older folks," and people wanting to restore their gun rights, and not the low-level non-violent drug offenders he's most concerned about.

USA TODAY reported last month that the average age of pardon cases granted by President Obama was at an all-time high, even as he's pardoned fewer people than any president since James Garfield was assassinated in 1881.

"In the African-American community, a big reason is you have young people with criminal records who are finding themselves unemployable. That's not just bad for them,. It's bad for their children, it's bad for the community," Obama said. "We've got to reexamine how sentencing is working, and make sure it's done equally by the way."

The White House has given special attention to historically black colleges and universities as part of an effort to increase the nation's college graduation rate. the Benedict College appearance was also an opportunity for Obama to promote My Brother's Keeper, a year-old effort to encourage mentoring programs for African-American young men.

The visit marked Obama's first trip as president to South Carolina, an early primary state Obama credits with helping him get elected in 2008..

"It's been a while since I've seen you," Obama said. "I love you, and I've been loving you. It's just that I've had a lot of stuff to do since I first saw you."