The first-ever attempt by US record-keepers to estimate the number of uncounted "law enforcement homicides" exposed previous official tallies as capturing less than half of the real picture.
"And so when you ask somebody: 'Oh, I need 14 years of data from you,' and they keep half their data in files in a room somewhere in boxes, and the other half is on a computer that doesn't associate, say, officer-involved shootings with vehicular homicides, or Tasers – you're asking them a lot".
The report estimated "an average of 928 law enforcement homicides per year" for the years in question, suggesting that the FBI's published count of 414 such deaths in 2009, for example, might be 124% off, while its count of 347 such deaths in 2005 might be 167% off.
"The homicides that were not justifiable, where a law enforcement officer is found guilty of homicide, there's no way to identify that," said Planty.
Morris indicated last month that the FBI had no plans to change how it publishes its "justifiable homicides" numbers, repeating that the bureau was required by law to report the figures.
"The most common of these requests concerned fraud, homicides, kidnappings, and other criminal investigations".
No law requires local agencies to fill out the reports, and some agencies do not, especially not for officer-involved homicides, according to experts who have studied the issue.
A separate tally of "arrest-related deaths", conducted by BJS itself, was slightly more accurate for the years in question, capturing 49% of law enforcement homicides, at best, the report found.
Even the two counting systems combined, as overseen by the FBI and BJS, missed an average of 263 homicides by law enforcement each year, BJS found.
A visitor to the FBI web page presenting the "justifiable homicides" figures, for example, encounters no caveat or disclaimer language of any kind.
The years under study saw several high-profile homicides by law enforcement of unarmed civilians, such as the 2009 shooting of Oscar Grant in a train station in Oakland, California – an episode that would become the subject of the award-winning film Fruitvale Station – and the 2006 killing of Sean Bell, who died in a hail of 50 bullets outside a nightclub in Queens, New York.
