The law was championed by Michael Bell after his son was shot by a police officer in Kenosha, Wis., in 2004.

Mr. Bell has met with Mr. Robinson’s family and offered advice. “I know what they are going through,” he said. “You’re walking around living your life and something like this happens. You’re overwhelmed, and you don’t know how to deal with the media and with the system. There’s no place where you can go and find out what to do when your son is shot by a police officer.”

Civil rights advocates are pushing for other states to enact policies similar to Wisconsin’s. Mr. Bell said that he receives phone calls and emails daily from lawmakers interested in passing similar legislation in their states.

Mr. Bell has praised officials for their handling of the case in Madison, but he says the law in Wisconsin does not go far enough. He is advocating for legislation that would require the outside investigation to be handed to an independent review board. The board would include those who have retired from law enforcement and also police academy instructors, with the aim of reducing future uses of excessive force.

When the law was just one week old in 2014, Dontre Hamilton was shot by a police officer in Milwaukee. As this Times video explains, it would be the first case to test how effective the new law is. Could it help provide a new faith in the justice system?