The U.S. Justice Department was already investigating the Cleveland Police when one of the division's officers gunned down a 12-year-old playing with a pellet gun last November. In his first national interview since that tragedy, Cleveland Police Chief Calvin Williams disagrees with parts of the Justice Department's report and defends his troubled force, saying the majority are good, but there are bad officers he is working hard to rid the division of and the bad reputation they have given it.

Bill Whitaker reports from Cleveland, where he accompanies the city's law enforcement officers on routine patrol and as they engage in community outreach for a story on the hot-button issue of policing in America. He also conducts the first sit-down interview with the family of a mentally ill woman killed in an altercation with Cleveland police officers. His story will be broadcast Sunday, Jan. 25 at 7 p.m. ET/PT.

"Of course there are [bad guys among Cleveland Police] and it's my job to make sure we weed out the bad people from this division and that we nurture and grow and support the good officers that are out there," says Williams.

He also aims to keep potentially bad operators off the force. The rookie officer who shot 12-year-old Tamir Rice had been deemed emotionally unfit by another police department. "Those are things that are under investigation," Williams tells Whitaker. "We know some of the things that happened in that process and we're...changing the way some of that is done."

In the Rice incident that made national headlines, the boy was shot dead within a few seconds of the arrival of the police cruiser. "A 12-year-old boy lost his life. Period," says Williams. "And what makes it even more difficult for me not just as a person who lives in the city but as a chief, is that that happened at the hands of a police officer."

The year before the Rice tragedy, Cleveland requested the Justice Department investigate its police after more than a 100 of them joined a high-speed chase of a vehicle whose engine backfire was mistaken for a gunshot. Two unarmed persons died inside the car; police fired at it 137 times. For that incident and others, the Justice Department report found a systemic pattern of "unnecessary and excessive use of deadly force." Williams denies the findings are systemic.

But Cleveland's top police officer does agree with some of the report's findings. "I agree that there are some issues within the Cleveland Division of Police as they pertain to the use of force...reporting and community issues," Williams says, alluding to a finding that his officers had a poor relationship with the community. "We are working diligently both with the Department of Justice and the community to make sure we correct these things," says Williams.