The police union praised Tuesday's announcement.
"We believe the district attorney's decision today to exonerate Officer Matthew Kenny was appropriate," Wisconsin Professional Police Association Executive Director Jim Palmer said in a statement. "The exhaustive, independent and transparent investigation into this tragic incident has confirmed that Officer Kenny's actions on the night of March 6 were lawful and in response to a deadly threat, from which Officer Kenny sustained numerous injuries, including a concussion.
But the decision not to charge Kenny drew swift criticism from several of Robinson's family members, who briefly spoke with reporters after meeting with the district attorney on Tuesday.
"This is politics, and not justice," grandmother Sharon Irwin said.
Andrea Irwin, the teen's mother, said she was so outraged when she heard the announcement that she had to leave the room.
"I'm heartbroken and I'm angry," she told CNN's Anderson Cooper. "I'm more than upset, almost something that I can't even describe right now."
Demonstrators chant near shooting site
Attorney Jon Loevy said the family's investigation into the case is continuing, but he declined to answer questions from reporters about it.
"We have more questions than you do," he said, "and we don't have answers."
Robinson's family supports protests over the case, but stresses they should not be violent, Loevy said.
"The family feels strongly that protests should not be violent, should be calm," he told reporters. "This is not a situation where people should get hurt or the community should tear itself apart."
Ozanne called for calm as he made his highly anticipated announcement.
"I am concerned that recent violence around our nation is giving some in our communities a justification for fear, hatred and violence," he said. "I am reminded that true and lasting change does not come from violence, but from exercising our voices and our votes."
The Police Department has said it prepared for the prosecutor's announcement for weeks and hoped to avoid violence and property damage.
"Unrest like we have witnessed elsewhere in our country cannot possibly aid in constructive engagement and only holds us back," Madison Police Chief Mike Koval said in a blog post responding to Tuesday's announcement
. "The environment for healing and reconciliation has been forged, owing to the incredible capacity of the Robinson family and their urging of the community to deal with the issues at hand with responsible activism."
Near the site of the March shooting, demonstrators held a large banner Tuesday that said, "BLACK LIVES MATTER" and chanted, "No justice, no peace, no racist police."
Prosecutor details investigation
As he revealed his decision, Ozanne noted his own background as the first district attorney of color in the state, then detailed the evidence that led him to the conclusion that Kenny should not be charged.
"My decision will not bring Tony Robinson Jr. back," Ozanne told reporters. "My decision will not end the racial disparities that exist in the justice system, in our justice system. My decision is not based on emotion. Rather, this decision is based on the facts as they have been investigated and reported to me."
Ozanne's announcement came after state authorities investigated the shooting. That's because of a Wisconsin law
that requires officer-involved killings to be investigated by officials from outside the law enforcement agency employing the officer involved in the death. A summary of findings from that investigation
was also released on Tuesday.
The district attorney detailed the series of three 911 calls dispatchers received on March 6 before Kenny arrived at the scene, toxicology results and Kenny's account of what happened that day.
Toxicology reports confirmed that Robinson had taken hallucinogenic mushrooms, marijuana and Xanax before the shooting, the district attorney said, and 911 calls reported that he was acting "insane" and attacking people.
Kenny was called to an apartment over reports that Robinson had been jumping in front of cars and assaulting people.
After hearing some commotion, Kenny entered the apartment.
Kenny reported that Robinson hit him and knocked him into the wall inside the apartment, an account that the prosecutor said was supported by damage to drywall.
After that, Kenny said he was afraid Robinson would hit him again or take his gun, and opened fire as the 19-year-old continued to come at him.
In three seconds, seven shots were fired.
All of them hit Robinson at close range, Ozanne said.
Mother: Family plans to file lawsuit
Robinson's mother said her family "absolutely" plans to file a civil lawsuit against the Police Department.
"The things that have taken place since my son passed and the things that have been done to my family, to me, they've gone above and beyond to try to make sure they kick me when I'm down," she said Tuesday. "They have done a smear campaign against my child and against me since this all began."
According to the Wisconsin State Journal, Robinson's friends and family members have said he took hallucinogenic mushrooms and was behaving erratically the day he was killed. They reject the idea that Robinson was a threat to Kenny when he was shot, the newspaper reported.
Robinson's uncle Turin Carter said in March that family members trusted state investigators to handle the case "with integrity."
But weeks later, the family publicly questioned whether the investigation would be fair.
And on Tuesday, they said Robinson had been unfairly demonized.
"I would just like everybody to keep in mind that this is a 19-year-old kid whose life was cut short before he was able to reach his full potential," Carter said.
Robinson's family has hired a Chicago law firm to carry out its own investigation into the shooting and commissioned a private autopsy, according to the Wisconsin State Journal.
Kenny has been on paid administrative leave since the shooting. That status will continue, the police chief said Tuesday, while the department completes an internal policy review of the incident.
Previous incidents drew attention
Both Kenny and Robinson had incidents in their past that attracted attention after the shooting.
In 2007, Kenny shot and killed
a man, Ronald Brandon, who was pointing a pellet gun at officers.
Kenny was exonerated of wrongdoing in that shooting and received a commendation.
Wisconsin Circuit Court documents indicate Robinson pleaded guilty in December to an armed robbery that occurred in April 2014.
Police Chief Koval and Madison Mayor Paul Soglin said in March that discussion of Robinson's record was inappropriate.
"The fact that Tony was involved in any kind of transgression in the past has nothing to do with this present tragedy," Soglin said.