(CNN) -- The mayor of North Chicago placed the city's police chief on leave and hired a retired officer to lead an investigation into six cases of alleged excessive use of force by police over the past 18 months.





Police Chief Michael Newsome is on paid administrative leave, Mayor Leon Rockingham Jr. said Tuesday.





"I do think that is something that we do need to look into and make sure that things are being done properly in our police department," Rockingham said. "There's a lot of things that have come to light that I think does warrant us to take a second look."





In addition, the gender and race of the people involved in the incidents will be investigated, and reporting requirements will be tightened, he said.





"I think that we, as the city of North Chicago, do need to make sure that the residents and people who are coming into our community are being handled properly," he said.





But Rockingham expressed confidence in police, whose job is to maintain order among the 36,000 residents of North Chicago, where the average income was $17,685, according to the 2010 Census.





"I will say, if there's anyone we find that is not doing what they should be doing, we will do disciplinary actions to those officers," he said. "But I think, all in all, if you look at our department, we have a fine police force."





Over the past four years, the department has been involved in some 88 use-of-force incidents, the mayor said. Asked how many of them were investigated at the time they occurred, Rockingham said that will be part of the newly announced investigation, which is to be completed by February 1.





Rockingham said the six cases came to light after publicity surrounding the November case of Darrin Hanna, who died days after police allegedly beat him and used a Taser on him during a domestic abuse call to his house.





"I'm a mother who lost her son by a beating," his mother, Gloria Carr, told reporters recently.





Lawyer Kevin O'Connor is representing Hanna's family and three other alleged victims in the cases under investigation.





O'Connor said the North Chicago Police Department has a problem with a group of officers that have repeatedly beat people.





"I think there are very good officers on the force, but it looks like the problem is in the night shift that is not very well supervised," said O'Connor. "There is about 10 that call themselves a gang. We have heard stories that they handcuff people and tell them they have a time period to run before they are beaten. So basically they are making them run, so that they can get a chance to beat them up."





O'Connor said his law firm has heard from more than 30 people who plan to come forward and tell their story about abuse from local police.





"They were scared before, but now they want to tell their stories," O'Connor said. "I am glad the mayor did this. This is the first step. But why did it take someone dying before someone finally did something?"





In a case that occurred last October, Christopher Harper, 31, of Waukegan, said he was preparing to leave his job as a bouncer at a North Chicago bar when a policeman pulled up shortly before midnight. The radio in Harper's Dodge Magnum was cranked, which apparently bothered the policeman, Harper said.





"He told me he was towing the car for loud music," Harper said.





Harper said he took his house keys out of his car's ignition and was walking away from the policeman toward the bar when he was struck repeatedly by electroshocks.





"He just Tased me in my back for no reason and kept doing it. I didn't understand that."





The officer fired a Taser at least six times into his back, he said.





"I ran 'til I couldn't take no more of the shockage, and then I just fell out. I was asking him why was he
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