Protests in Wisconsin after prosecutor ruling on Tony Robinson shooting
Photo of 19-year-old Tony Robinson Jr., who was shot and killed by a Madison, Wisconsin police officer on March 7. (NBC News)

Hundreds of people protested Wednesday in Wisconsin's capital, blocking a road a day after a prosecutor ruled that a Madison police officer's fatal shooting of an unarmed biracial teenager was justified.

Relatives of Tony Robinson, 19, had expressed disappointment at Dane County District Attorney Ismael Ozanne's decision on Tuesday that Madison officer Matt Kenny, who is white, used justified lethal force in the March 6 shooting.

More than two dozen people were arrested, mostly on suspicion of obstructing the road, and then released, Madison Police spokesman Joel DeSpain said, describing their acts as peaceful civil disobedience.

Demonstrators marched from the house where Robinson was shot to a courthouse and a jail.

Protesters in Minneapolis, Minnesota, marching in solidarity with their Madison counterparts on Wednesday night said on social media that police used mace against demonstrators, including a 10-year-old boy.

Minneapolis Police Chief Janeé Harteau in a statement late on Wednesday night promised a "thorough investigation" of the allegations.

Robinson's shooting was one of several officer-involved deaths that have led to increased scrutiny of police use of force, particularly against young black men.

Brandi Grayson, co-founder of the Young Gifted and Black Coalition that organized the protest, said the group wanted community control over the hiring and firing of officers and a U.N. probe into racial disparities in Dane County and Wisconsin.

"We don't have time-set goals. We understand the struggle for black liberation will be generational," Grayson said.

Lakaya Horton, 13, of Madison, got permission to go to the protest with her mother and a friend instead of school.

"No matter who you are, you should be charged for killing a person," Horton said.

Ozanne said Kenny was responding to multiple emergency calls reporting that a man had battered someone and was dodging traffic in the street. Robinson's friends called 911 to say they were afraid of him because he was acting violently and was on drugs.

Robinson struck the officer in the head and Kenny shot Robinson seven times, Ozanne said. Robinson had psilocybin mushrooms, marijuana and the psychoactive drug Xanax in his system, he said.

There were large but orderly demonstrations in Madison after Robinson's shooting. The city of 240,000 people is nearly four-fifths white and 7 percent African-American, according to U.S. Census figures.

Attorney Jon Loevy, who represents Robinson's family, said on Tuesday the decision left many unanswered questions.

Kenny is on paid administrative leave pending completion of a department internal investigation.

(Story corrects spelling of Wisconsin in headline)