Brown’s death sparked weeks of racially charged protests, and elevated to national debate the issues of discriminatory policing — which refers to law enforcement targeting individuals based on factors including race, religion, or age — and whether minorities are more often killed by police officers.

But activists and researchers say the way the FBI collects data under its Uniform Crime Reporting (UCR) Program makes it impossible to know exactly how many Americans are killed by law enforcement officials each year. Local and state departments only report such information on a voluntary basis, according to an emailed statement from FBI Relief Media Liaison Billy Estok.

The FBI only categorizes what it terms an “officer-involved homicide” differently from other homicides if a policeman killed a felon in the line of duty, in which case the FBI classifies it as a “justifiable homicide.” The FBI’s existing database does not include information on every incident of someone being killed by law enforcement, nor data beyond a count of justifiable homicides — which in 2012 amounted to 410, Estok said.

Activists have called on federal agencies to create a national public database of police shootings, use of excessive force, misconduct complaints, arrests and more — all broken down by race and other demographic factors, Nelson told Al Jazeera.

Other demands include a fully resourced DOJ investigation into discriminatory policing and excessive force, an end to federal grants that encourage police militarization, and an executive order to form an enforceable prohibition on police brutality and discriminatory practices.

“This brings together cries for local justice (in Ferguson) with pressure to federal agencies to move on the concrete reforms necessary for policing nationwide,” Nelson said.

A number of publications have reported on the lack of comprehensive national data on police killings, echoing Color of Change’s complaints of incomplete information.

ProPublica news website writer Ryan Gabrielson — whose recent article, “Deadly force, in black and white,” delved into the lack of available information — said he had known from previous research that certain data sets on the topic “weren’t that good.”

“But then we had a crash course in how incomplete the data is,” he said. “Every data set has its problems and weaknesses, but these are particularly pronounced and it seems like something we should record more accurately.”

Another journalist, D. Brian Burghart of Reno News and Review, decided to create his own database through a website he created, called Fatal Encounters. It allows individuals to make public records requests in their own areas and send the information to the website — effectively crowd-sourcing the data.

“I just couldn’t believe that this information didn’t exist — not just for journalists — but for the public,” Burghart said.

Gabrielson said he and other ProPublica reporters gathered 33 years’ worth of supplementary homicide data from the FBI and poured over it for weeks to look for trends and identify what information was missing.

He said there were “plenty” of holes, with some states, such as Florida, not reporting data on officer-involved homicides to the FBI for almost 20 years. Of more than 17,000 law enforcement agencies in the U.S., Burghart said his research indicated that only about 1,000 contribute data on officer-involved homicides.

“Some states/agencies do not report justifiable homicide data … some justifiable homicide data are missing such as the entire states of New York and Florida,” while “only two agencies, Chicago and Rockford, report justifiable homicide data in Illinois,” Estok of the FBI said in an email.

Gabrielson and his team decided to turn the numbers that were available into rates and ratios, which he said could expose trends in police violence. They found that black males between the ages of 15 and 19 were 21 times more likely to be killed by a police officer than white males in the same age group.

“It blew us away,” Gabrielson said, noting that this rate had a margin of error because of the scant reporting available — but he said it was still clear that black teenage males were at significantly higher risk than any other demographic.

Burghart said he also reached some startling conclusions based on data he has compiled on Fatal Encounters. In states for which he had comprehensive data, the percentage of homicides carried out by law enforcement officers was 7.4 percent. His findings echo a recent report by the Youth Justice Coalition, a California-based organization working to reform Los Angeles’ juvenile justice system. It found that the percentage of homicides carried out by police in Los Angeles county more than doubled from 3 to 7 percent between 2000 and 2014.

“That’s an incredible number that should be national news by itself,” Burghart said. “There’s more police homicides than gang homicides.”

The FBI’s most recent general homicide data shows that law enforcement agencies reported 720 incidents in which Americans were killed by police in 2012 — but that figure does not include officer-involved homicides that were not voluntarily reported. By contrast, in the past two years German police have killed a total of eight people and British police have killed none.

“The tragic shooting of Michael Brown has touched the hearts of many … and has activated and energized a new generation of leaders who are saying ‘Enough is enough,’” Nelson said. “In addition to the constant threat and fear about losing their child to it — it could be an unjust stop and frisk or arrest that quickly turns violent and deadly — that’s some of the motivation behind what we’re doing.”