Protesters with "The Hands Up Coalition DC" hold placards in front of the U.S. Justice Department in Washington Dec. 22, 2014. Reuters/Larry Downing

Family members of Dontre Hamilton, a black Milwaukee man who was shot and killed by a white police officer, hope that a federal investigation into the case may lead to charges against former Officer Christopher Manney. Milwaukee County District Attorney John Chisholm had announced Monday that Manney will not be charged in the fatal shooting of the unarmed man.

The justice department announced that it will review whether Manney violated federal civil rights laws during the April incident. Hamilton's brother, Nate Hamilton, said the family hopes federal investigators can weigh all the evidence in the case and charge the officer in the death of the 31-year-old, The Associated Press reported. Nate said the family questioned the objectivity of the state's Division of Criminal Investigation in reviewing the case because it has worked closely with Milwaukee police in the past.

"I think we'll get a better look. I want to be confident in it, but, right now, I cannot put my trust in the system," Nate reportedly said.

Hamilton was shot 14 times by Manney after the officer responded to a call of a man sleeping in a park. Several witnesses in the case reportedly told local police that they saw Hamilton holding Manney’s baton aggressively before the officer shot him. Chisholm reportedly said that Manney acted in self defense when he shot Hamilton. His report also revealed that Manney suffered minor injuries, including a bite to his right thumb, and added that the two also exchanged punches.

Hamilton's family had reportedly said that he suffered from schizophrenia and had stopped taking his medication. Chisholm said that his decision in the case took so long because he decided to consult with use-of-force experts, who concluded that Manney’s actions were justified.

Manney was fired by Milwaukee Police Chief Edward Flynn in October for not following department rules. "This intentional action, in violation of training and policy, instigated a physical confrontation that resulted in a deadly use of force," he said.

The decision not to charge Manney came two days after two New York City police officers were shot and killed by a black man who claimed they were revenge killings for the deaths of Michael Brown and Eric Garner. The decision also sparked a silent march Monday outside the federal courthouse in Milwaukee, while some protesters forced the closure of a local mall.

Hamilton’s family urged protesters to remain peaceful, while Nate said that the family had "cried too long" and "we don't have to be the voice of reason.

"We need to stop the violence in our communities so we can get rid of these pigs that kill us," he said, according to AP. "Because that's what they are. They feed, they feed off of us. And we can't let them do that no more."

Authorities in the United States have come under fire over the use of excessive force by police after officer-involved killings of black men in recent months, which have triggered days of unrest across the nation. Both the officers involved in the Brown and Garner cases have not been criminally charged.