With every video that surfaces of questionable or shocking police conduct, at least two questions arise. The first is how exactly each incident happened. The second is how common such incidents are. The first question can be addressed though investigation, which can surprise both police and their critics, and eventually through better training. The second question is more straightforward - and the lack of an answer is unacceptable. The U.S. Department of Justice actually has two separate counts of deaths in police custody - one by the Federal Bureau of Investigation, and one by the Bureau of Justice Statistics. Each count misses half of all deaths; the department hoped that by combining them, it would get a reasonably accurate number. Its hope was misplaced. The department pretty much acknowledges that its number is unreliable. The Bureau of Justice Statistics suspended its data collection more than a year ago and has since been examining ways to improve the accuracy of its count. A law passed last December with strong bipartisan support allows the attorney general to withhold up to 10 percent of some federal grants to states if they fail to comply with reporting requirements. The law gives states 120 days to begin reporting deaths on a quarterly basis, but the department will not set any requirements for reporting until it completes an internal review of its own data collection. Better numbers won't solve the problem. But they can be a useful gauge through which to measure and focus any proposed solution.