People march in Washington on Sept. 6 to protest the killing of Michael Brown. (Nicholas Kamm/AFP/Getty Images)

A summer of high-profile police shootings, most notably the Aug. 9 shooting of 18-year-old Michael Brown in Ferguson, Mo., has rekindled a decades-long debate over law enforcement’s use of lethal force.

Police unions and some law-and-order conservatives insist that shootings by officers are rare and even more rarely unjustified. Civil rights groups and some on the left have just as quickly prescribed racial motives to the shootings, declaring that black and brown men are being “executed” by officers.

And, like all previous incarnations of the clash over police force, the debate remains absent access to a crucial, fundamental fact.

Criminal justice experts note that, while the federal government and national research groups keep scads of data and statistics— on topics ranging from how many people were victims of unprovoked shark attacks (53 in 2013) to the number of hogs and pigs living on farms in the U.S. (upwards of 64,000,000 according to 2010 numbers) — there is no reliable national data on how many people are shot by police officers each year.

The government does, however, keep a database of how many officers are killed in the line of duty. In 2012, the most recent year for which FBI data is available, it was 48 – 44 of them killed with firearms.

But how many people in the United States were shot, or killed, by law enforcement officers during that year? No one knows.

Officials with the Justice Department keep no comprehensive database or record of police shootings, instead allowing the nation’s more than 17,000 law enforcement agencies to self-report officer-involved shootings as part of the FBI’s annual data on “justifiable homicides” by law enforcement.

That number – which only includes self-reported information from about 750 law enforcement agencies – hovers around 400 “justifiable homicides” by police officers each year. The DOJ’s Bureau of Justice Statistics also tracks “arrest-related deaths.” But the department stopped releasing those numbers after 2009, because, like the FBI data, they were widely regarded as unreliable.

“What’s there is crappy data,” said David A. Klinger, a former police officer and criminal justice professor at the University of Missouri who studies police use of force.

Several independent trackers, primarily journalists and academics who study criminal justice, insist the accurate number of people shot and killed by police officers each year is consistently upwards of 1,000 each year.

“The FBI’s justifiable homicides and the estimates from (arrest-related deaths) both have significant limitations in terms of coverage and reliability that are primarily due to agency participation and measurement issues,” said Michael Planty, one of the Justice Department’s chief statisticians, in an email.

Even less data exists for officer-involved shootings that do not result in fatalities.

“We do not have information at the national level for police shootings that result in non-fatal injury or no injury to a civilian,” Planty said.

Comprehensive statistics on officer-involved shootings are also not kept by any of the nation’s leading gun violence and police research groups and think tanks.

In fact, prior to the Brown’s shooting, the only person attempting to keep track of the number of police shootings was D. Brian Burghart, the editor and publisher of the 29,000-circulation Reno News & Review, who launched his “Fatal Encounters” project in 2012.

“Don’t you find it spookey? This is information, this is the government’s job,” Burghart said. “One of the government’s major jobs is to protect us. How can it protect us if it doesn’t know what the best practices are? If it doesn’t know if one local department is killing people at a higher rate than others? When it can’t make decisions based on real numbers to come up with best practices? That to me is an abdication of responsibilities.”

Burghart has enlisted a team of volunteers to search news clips as well as file records requests for data, with the goal of collecting a database that will chronicle several years-worth of police shootings.

As of September 1, according to Burghart’s estimates, 83 other people had been killed by police officers in the United States since Michael Brown’s death.

Law enforcement watchdog groups and think tanks say that the lack of comprehensive data on police shootings hampers the ability of departments to develop best practices and cut down on unnecessary shootings.

The way we improve practices is to take information about what’s happening in the field to make those improvements,” said Chuck Wexler, executive director of the Police Executive Research Forum, a nonpartisan think tank in D.C. that produces reports on police tactics. “The more we know about (the number of officer-involved shootings) the better off we’ll be.”

Other than basic statistical analysis, Wexler said, a comprehensive database of police shootings would allow departments to better analyze when officers are drawing and using their guns – potentially leading to policy changes that could save lives.

He noted a shift in policy by the New York Police Department in 1972, in which the department instructed its officers to no longer shoot at moving vehicles.

“When they made that change the number of NYPD shootings plummeted,” he said.

James O. Pasco, the national executive director of the Fraternal Order of Police, believes that an accurate database would require Congress to pass a law requiring police departments to report their shooting data to a federal agency, presumably the FBI.

“Otherwise it’s an unfunded mandate,” Pasco said. “About 80 percent of police departments have fewer than 10 officers. They don’t have huge data collecting operations. They don’t even have a single person in some of these departments who are dedicated to all the statistical work they have to do now.”

Pasco said he doesn’t know what the union’s position would be on a legal requirement to report shootings and the result of shooting investigations.

“It would depend on what the law looked like,” he said. “Clearly, if it’s just a function of collecting the data, I can’t see that we would have a problem with that. Our issues are with due process for officers.”

The most detailed analysis of police shootings to date was conducted by Jim Fisher, a former FBI agent and criminal justice professor who now authors true crime books.

“I was rather surprised to find there are no statistics,” Fisher said. “The answer to me is pretty obvious: the government just doesn’t want us to know how many people are shot by the police every year.”

In 2011, he scoured the Internet several times a day every day, compiling a database of every officer-involved shooting he could find. Ultimately, he tracked 1,146 shootings by police officers, 607 of them fatal shootings.

“I was surprised at how many shootings, a reasonable person would conclude, were unnecessary,” Fisher said.

Earlier this year, the Gawker Media-owned sports Web site Deadspin launched a project to crowd-source a definitive list of police shootings by analyzing local media reports – a system modelled off of Fisher’s 2011 effort.

“Having that data would be extremely helpful, in more ways than one,” said Adolphus M. Pruitt, president of the St. Louis chapter of the NAACP, who has been one of those most vocal about allegations of police brutality in light of Brown’s shooting. “We track everything. There is no reason in the world for us to not be able to know just how many people the police are shooting in any given year.”

In the absence of reliable data, the FBI’s “justifiable homicides” statistics continues to be widely cited in academic studies, media reports, and other examinations of the use of lethal force by law enforcement despite being decried as unreliable by officials inside the Justice Department and other officials outside of the government.

As they do, criminal justice experts note that even compiling accurate numbers of people shot and killed by the police would be just a start.

“Every study that I’m aware of shows that most of the people who are shot by the cops survive and most of the time when cops shoot the bullets don’t hit,” said Klinger, who will soon publish a new study analyzing police shootings in St. Louis.

That study, prepared with several other academics, found that there were 230 instances in the City of St. Louis between 2003 and 2012 when officers fired their weapons. Only 37 of those fired upon were killed.

“If your statistics look just at dead bodies you’d be under-counting it by 85 percent,” Klinger said. “If the cops are shooting, we need to now when they are shooting, not just when they kill somebody with the bullets.”

Kimberly Kindy contributed to this report.