The day after the U.S. Department of Justice said it's planning a civil rights investigation of the Ferguson, Missouri, police department, the police chief said, "We've done an excellent job, [but] we can be better and we're willing to be."

Ferguson Police Chief Thomas Jackson spoke with NBC News on Thursday, after the Justice Department said it would be investigating the circumstances surrounding the shooting of teenager Michael Brown by a Ferguson police officer, as well as years of officer conduct.

Last month's shooting set off day of intense protests in that community, which has a history of racial tension. Brown, who was black, was shot by white police officer Darren Wilson.

"It's not for me to tell them that they shouldn't do it," Jackson said of the investigation. "There's a desire for questions to be answered about this case and I understand that." He added that his officers will cooperate fully with investigators.

Jackson said his force has had "good dialogue" recently with Ferguson residents and that most of the town's residents would say "our relationship with the community is excellent."

Ferguson Mayor James Knowles said that the investigation into this city's police force didn't worry him.

"(I'm) absolutely interested in wanting to know the truth of what's been going on," he said. "I feel that we've been making extremely positive strides in making sure that we have policies and procedures in place that not only protect and serve our citizens, but also protect their civil rights."

A Justice Department official said the investigation not only will look at Ferguson police, but other police departments in St. Louis County, many of which are -- like Ferguson -- largely white forces serving largely black communities, The Washington Post reported.

This investigation is on top of a probe into whether Wilson acted in violation of Brown's civil rights and will look at patterns of police behavior to see if any trends can be found.