Brazil, with more than 60,000 homicides per year, has one of the highest levels of impunity in the world, as only 8 percent of murders lead to criminal convictions, anti-violence NGO Rio de Paz said Wednesday.
"Ninety-eight percent of murders in Germany are punished. In Japan, more than 95 percent. But in Brazil only 8 percent of homicides are solved," Rio de Paz founder Antonio Carlos Costa told EFE.
He pointed to the murder a year ago of human rights activist and Rio city councilor Marielle Franco, which remains unsolved, though authorities arrested two ex-cops on Tuesday in connection with the case.
The 38-year-old Afro-Brazilian LGBT woman and her driver, Anderson Gomes, were fatally shot on March 2014.
One of the people arrested Tuesday is charged with being the shooter, while the other is accused of driving the car used in the attack.
Authorities have yet to determine who masterminded the crime.
"We want to know who ordered Marielle's murder. We want to know who were the intellectual authors of that crime. That murder exists in a very large context of impunity, as do the majority of homicides in Brazil," Costa said.
He said that the failure of law enforcement and the justice system to solve crimes encourages criminals to continue doing harm, because "whoever kills, whoever orders a killing, knows he will not be punished."
"We want measurable goals, a timetable and a commitment from the minister of justice" to reduce Brazil's homicide rate from the current 30 murders for every 100,000 inhabitants, Costa said.
To dramatize their argument, Rio de Paz erected a giant cage in Rio de Janeiro's Cinelandia square: an empty cell to symbolize impunity.
The cell was decorated with messages in both English and Portuguese, such as "Who ordered Marielle's murder?" and "Prison empty, but the street covered in blood."
Separately, representatives of Amnesty International held an event in Rio on Wednesday to mark the one-year anniversary of Franco's murder.
The directors of the US and Brazilian branches of AI, Margaret Huang and Jurema Werneck, respectively, and the slain politician's mother, Marinete Silva, appeared in front of the Rio de Janeiro state government building with an installation of boxes marked with letters spelling out "Who killed Marielle?"
The boxes contained petitions with the signatures of 778,000 people from around the world demanding justice for Franco.