A 19-year-old black man who died after being shot by a white police officer was unarmed, the Madison police chief said Saturday, assuring protesters who earlier in the day had chanted "Black Lives Matter" that his department would defend their rights to gather while imploring the community to express their anger with "responsibility and restraint."

Tony Robinson was shot Friday night after assaulting Officer Matt Kenny, Madison Police Chief Mike Koval said. Kenny was injured, Koval said, but didn't provide details. It wasn't clear whether Robinson, who died at a hospital, was alone in the apartment.

"He was unarmed. That's going to make this all the more complicated for the investigators, for the public to accept," Koval said during a news conference. Police department spokesman Joel DeSpain said Kenny would not have been wearing a body camera.

Several dozen protesters gathered earlier Saturday outside of the Dane County Public Safety Building holding signs that read "Black Lives Matter" — a slogan adopted by activists and protesters around the U.S. after recent officer-involved deaths of unarmed blacks — before walking toward the neighbourhood where the shooting took place. Protesters also shouted the slogan Friday night.

Killings by Police-Madison

Madison Police Chief Mike Koval asked people to protest peacefully. (Steve Apps/Wisconsin State Journal/Associated Press)

Koval, who struck a conciliatory tone during Saturday's news conference, said he understood the anger and distrust taking hold in the community and that "for those who do want to take to the street and protest," his department would be there to "defend, facilitate, foster those First Amendment rights of assembly and freedom of speech."

He also asked protesters to follow what he said was the lead of Robinson's family in asking for "nondestructive" demonstrations.

Officer involved in 2007 shooting

Kenny has more than 12 years of experience, Koval said, and was involved in a 2007 shooting but was cleared of any wrongdoing because it was a "suicide by cop-type" situation. He has been placed on administrative leave pending the results of this investigation by the state's Division of Criminal Investigation and the Dane County District Attorney's review of that investigation.

A 2014 Wisconsin law requires police departments to have outside agencies probe officer-involved deaths after three high-profile incidents within a decade — including one in Madison — didn't result in criminal charges, raising questions from the victims' families about the integrity of the investigations.

State Attorney General Brad Schimel said the department will not share details of the investigation until it is finished. "We are resolved that the result of that investigation will be one in which the public can have confidence," he added.

The shooting came days after the U.S. Justice Department cleared Darren Wilson, the white former Ferguson, Mo., officer who shot and killed 18-year-old Michael Brown, who was black and unarmed, of federal civil rights charges. A second report found patterns of racial profiling, bigotry and profit-driven law enforcement and court practices in the St. Louis suburb.

Madison, about 130 kilometres west of Milwaukee, is the state capital and home to the University of Wisconsin's flagship campus. About seven per cent of the city's 243,000 residents are black.

Killings by Police Madison

Madison Police guard the home where Tony Robinson reportedly had an altercation with an officer. (Steve Apps/Associated Press)

Koval said police responded to a call about 6:30 p.m. Friday of a person jumping into traffic. A second call to police said the man was "responsible for a battery," Koval said.

Kenny went to an apartment and forced his way inside after hearing a disturbance. Koval said the officer was assaulted by Robinson, and then fired at him.

Grant Zimmerman, a neighbour of Robinson's, said Robinson would run between his apartment and his roommate's mother's house across the street "all the time, even in the middle of traffic."

Late Saturday afternoon, people filled the Fountain of Life Covenant Church for a community meeting. Family members took the stage and read a statement prepared by Robinson's mother, Andrea Irwin.

"I can't even compute what has happened," Irwin's statement said. "I haven't even had a chance to see his body."

She was not present, and the statement said she was taking time to grieve with her children. Robinson's grandmother, Sharon Irwin, was on the stage as the statement was read, but left immediately after.

Robinson, a 2014 graduate of Sun Prairie High School, was well-liked, according to Olga Ennis, a neighbour and family friend. "He wouldn't hurt a fly," Ennis said.

She said many in the community don't trust police officers. "We're afraid of the cops," she said. "Who do you call for help now?"

Koval, who said he went to Robinson's mother's house overnight and spoke with the 19-year-old's grandparents, expressed his sympathy Saturday, saying, "19 years old is too young."