Ferguson, Mo. Cleveland, Ohio. Staten Island, N.Y. Eutawville, S.C..

In each place, individuals - all unarmed except for a child carrying a pellet gun - died at the hands of police officers. All of the dead were black. The officers involved, white.

To many Americans, it feels like a national tidal wave. And yet, no firm statistics can say whether this spate of officer-involved deaths is a growing trend or simply a series of coincidences generating a deafening buzz in news reports and social media.

"We have a huge scandal in that we don't have an accurate count of the number of people who die in police custody," says Samuel Walker, emeritus professor of criminal justice at the University of Nebraska at Omaha and a leading scholar on policing and civil liberties. "That's outrageous."

There are some raw numbers, but they're of limited value.

The FBI's Uniform Crime Reports, for instance, track justifiable police homicides - there were 1,688 between 2010 and 2013 - but the statistics rely on voluntary reporting by local law enforcement agencies and are incomplete. Circumstances of the deaths, and other information such as age and race, also aren't required.

The Wall Street Journal, detailing its own examination of officer-involved deaths at 105 of the nation's 110 largest police departments, reported last week that federal data failed to include or mislabeled hundreds of fatal police encounters.

Put simply: It's hard to know for certain what is happening on the ground.

"We want a comprehensive picture ... so people can be aware of what really goes on, and not the claptrap put out by people with agendas," says David Klinger, a professor of criminology at the University of Missouri-St. Louis who has studied use of deadly force and hopes to get funding for a pilot project that could provide better national statistics.

To those who have taken to the streets to protest in recent weeks, that lack of context is almost beside the point.

"These are communities that have been living for generations under the yoke of what has felt like an occupying force," says Phillip Atiba Goff, co-founder of UCLA's Center for Policing Equity. "And regardless of what any of the stats are ever going to say, if we don't address the reality of that experience, then we're shooting ourselves in the foot in our attempts to make good on our promise of democratic principles."

The high-profile cases have erupted one after the other.

On July 17, 43-year-old Eric Garner died after officers tried to arrest him on suspicion of selling untaxed cigarettes on a New York City street. Cellphone video captured the scene as one officer wrapped his arm around Garner's neck, and the black man repeatedly pleaded, "I can't breathe."

Tensions escalated on Aug. 9, when Officer Darren Wilson fatally shot unarmed, 18-year-old Michael Brown in the St. Louis suburb of Ferguson.

On Nov. 22, a Cleveland officer shot and killed 12-year-old Tamir Rice after responding to reports of an armed man at a city park. Rice had been holding a pellet gun.

Two days later, officials announced that a grand jury had declined to return an indictment in the Brown case. Fires from the resulting protests in Ferguson had barely stopped smoldering when word came there would be no charges against the officer in New York City. Again, angry protesters marched.

Then a grand jury in Orangeburg County, South Carolina, returned a murder indictment Wednesday against a former small-town police chief in the May 2011 shooting death of an unarmed black man.