Story byKimberly Kindy,Marc Fisher,Julie Tate,Jennifer Jenkins

The killing of an unarmed black man by a white police officer last year in Ferguson, Mo., ignited a national debate and exposed the federal governments failure to track the use of deadly force by police. The Washington Post launched a comprehensive project to log everyon-duty fatal shooting by police in 2015. Theresulting databasechronicled shootings nationwide in real time, using news reports and other public sources. The Post compiled data about each death, including the race of those killed, whether they were armed and descriptions of the events. The project revealed that police nationwide were killing morethan twice as many people as the FBI had previously reported. In October, the agencys director, James B. Comey, said it was unacceptable that journalists had become the leading source of information on the subject. In December, an FBI official told The Post the agency is overhauling how it tracks violent police encounters, calling it the highest priority. The Post will continue tracking fatal shootings by police in 2016.

Nearly a thousand times this year, an American police officer has shot and killed a civilian.

When the people hired to protect their communities end up killing someone, they can be called heroes or criminals a judgment that has never come more quickly or searingly than in this era of viral video, body cameras and dash cams. A single bullet fired at the adrenaline-charged apex of a chase can end a life, wreck a career, spark a riot, spike racial tensions and alter the politics of the nation.

In a year-long study, The Washington Post found that the kind of incidents that have ignited protests in many U.S. communities most often, white police officers killing unarmed black men represent less than 4 percent of fatal police shootings. Meanwhile, The Post found that the great majority of people who died at the hands of the police fit at least one of three categories: they were wielding weapons, they were suicidal or mentally troubled, or they ran when officers told them to halt.

The Post sought to compile a record of every fatal police shooting in the nation in 2015, something no government agency had done. The project began after a police officer shot and killed Michael Brown in Ferguson, Mo., in August 2014, provoking several nights of fiery riots, weeks of protests and a national reckoning with the nexus of race, crime and police use of force.

Race remains the most volatile flash point in any accounting of police shootings. Although black men make up only 6percent of the U.S. population, they account for 40percent of the unarmed men shot to death by police this year, The Posts database shows. In the majority of cases in which police shot and killed a person who had attacked someone with a weapon or brandished a gun, the person who was shot was white. But a hugely disproportionate number 3 in 5 of those killed after exhibiting less threatening behavior were black or Hispanic.

Regardless of race, in more than a quarter of cases, the fatal encounter involved officers pursuing someone on foot or by car making chases one of the most common scenarios in the data. Some police chiefs and training experts say more restrictive rules on when to give chase could prevent unnecessary shootings.

Like a growing number of police shootings, the death of David Kassick on a snow-covered field near his sisters house in Hummelstown, Pa., was captured on video a technological shift that has dramatically altered how Americans perceive officers use of deadly force.

In two minutes and 10 seconds of harrowing footage, the Kassick video serves as an almost perfect Rorschach test in the national debate over when it is justifiable for an officer to take a life.

Shots fired

Officer Lisa Mearkle has chased Kassick, first by car, then on foot. Now shes zapped him with her Taser and hes writhing on the ground, on snow, jammed up against a line of trees.

Viewed through the camera attached to the officers Taser, Kassick reacts to each of three shocks from the stun gun. Mearkle, screaming, orders Kassick, who is already involuntarily on the ground, to Get on the ground! Get on the ground!

Okay, okay, he responds.

As the officer stands over Kassick, repeatedly ordering him to Lie down and Show your hands, the 59-year-old does just that. He moans in pain, pulls his right hand out from under his head and stretches to display the hand.

But three times during the video, Kassick also does other things with his hands. As he says Okay, okay to the officers command, he also reaches toward his jacket pocket. A little later, his left hand moves toward his front pants pocket. He appears to be trying to remove Taser wires from his clothing. Thirty seconds later, he uses his left hand to lift himself slightly from the snow.

At the 1:39 mark, theres a pop and Mearkle says, Shots fired.

Within seconds, Kassick is flat on his stomach. He lifts his head. The officer, calm now, says, Keep your hands where I can see them.

The video ends. Kassick is dead, shot twice in the back.

He was unarmed.

Mearkle had given chase after Kassick fled from her attempt to pull him over for having an expired inspection sticker on his car.

The video age

In todays tinderbox of public concern about police brutality, video of shootings can be damning evidence or a clear defense. Police chiefs and politicians like video because in most cases it absolves officers of allegations of wrongdoing. Civilians like video because when officers do act abusively, digital proof makes coverups unlikely.

In the Kassick case, some of Mearkles defenders argue that intricate inspection of videos warps perceptions of the challenges police face. A system in which officers make split-second decisions but in which their bosses, prosecutors, jurors and the public have the luxury of examining every frame of video is unfair, said Les Neri, president of the Pennsylvania Fraternal Order of Police.

We now microscopically evaluate for days and weeks what they only had a few seconds to act on, Neri said. People always say, They shot an unarmed man, but we know that only after the fact. We are criminalizing judgment errors.

The decisions police officers must make in a flash can have fatal consequences for themselves as well as for suspects. Thirty-six officers have been shot and killed in the line of duty this year, according to theOfficer Down Memorial Page.

The widespread availability of video of police shootings from bystanders smartphones as well as from police body and dashboard cameras has been a primary factor in the rising number of indictments of officers.

Prosecutors cited video evidence against officers in 10 of the 18 felony cases filed against officers this year twice as often as video played a role in prosecutions over the previous decade, The Post found.

Thank God for technology, said the Rev. Ira Acree, pastor at Greater St. John Bible Church in Chicago, where Officer Jason Van Dyke faces a first-degree murder charge for shooting 16 rounds and killing Laquan McDonald, a 17-year-old who was walking down the middle of the street holding a three-inch knife. Maybe its finally helping us crack the blue code of silence.

After police dash-cam video of the 2014 incident was released last month, Mayor Rahm Emanuel (D) fired the citys police chief.

In the past, an officers word was not challenged, said Philip M. Stinson, a criminologist at Bowling Green State University who studies arrests of officers. If anything has shifted this year, its that. They are facing the kind of scrutiny the rest of us face when we kill someone.

But some officers friends and attorneys attribute the uptick in prosecutions to rising political pressure. On a fundraising website, supporters of West Monroe, La., officer Jody Ledoux blamed his January felony negligent-homicide indictment on our countrys current climate towards police. Ledouxs attorney, Mickey DuBos, did not return calls seeking comment.

Ledoux killed Raymond Martinez, a homeless 51-year-old, the day after a grand jury in New York City declined to bring criminal charges against Officer Daniel Pantaleo, who was recorded last year putting a fatal chokehold on Eric Garner, a Staten Island man who was stopped for selling loose cigarettes. The decision not to charge Pantaleo sparked nationwide protests.

Surveillance video in the Louisiana case shows Ledoux shot Martinez as he reached into a newspaper vending machine in front of a convenience store to retrieve his cellphone. Ledoux said he feared Martinez was reaching for a gun.

Although more officers were indicted in shooting cases this year, the outcome of such cases improved for officers. Five of the seven cases tried this year ended with the officer acquitted or with a mistrial. In two cases, charges were dismissed. Over the previous decade, one-third of officers charged in shooting cases were convicted of crimes ranging from misdemeanor reckless discharge of a firearm to felony murder.

This year, only one officer, Richard Combs, former chief of a small department in Eutawville, S.C., pleaded guilty. In September, following two mistrials on a murder charge, he pleaded to a misdemeanor charge of misconduct in office and was sentenced to one year of home detention after he fatally shot Bernard Bailey in a parking lot. Bailey had resisted arrest on a warrant in 2011.

As protests have increased pressure for transparency about fatal shootings, more departments have moved to equip officers with body cameras. Many chiefs say the cameras boost public confidence in the police, but most departments do not yet use them. About 6percent of fatal shootings this