About this story: 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 government’s failure to track the use of deadly force by police. The Washington Post launched a comprehensive project to log every on-duty fatal shooting by police in 2015. The resulting database chronicled 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 more than twice as many people as the FBI had previously reported. In October, the agency’s 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.

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 6 percent of the U.S. population, they account for 40 percent of the unarmed men shot to death by police this year, The Post’s 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.