This will take a great deal of careful research, partly because it will require judging the accuracy of "official sources." The FBI's Law Enforcement Officers Accidentally Killed 2004 breaks down the statistics of officers killed: (click title of answer for more)
"In the 10-year period 1995 through 2004, 717 law enforcement officers died from accidents occurring in the line of duty. Of these officers, 404 were killed in automobile mishaps, 120 were killed after they were struck by vehicles, 60 were killed in motorcycle accidents, and 43 lost their lives in aircraft accidents. In addition, 28 of the officers were mistakenly shot, 21 drowned, 20 died from falls, and 21 of the officers lost their lives in other situations. (See on Table 59.)"
But Table 59 gives no details of rank or race, etc. of the shooter. It does specify that these are nationwide figures for officers killed while on duty:
"Methodology: This section includes data regarding the accidental deaths of duly sworn local, state, tribal, and federal law enforcement officers meeting the same criteria as the officers who were feloniously killed: at the time of these incidents, the officers were working in an official capacity, they had full arrest powers, they were wearing a badge (ordinarily), they were carrying a firearm (ordinarily), and they were being paid from government funds set aside specifically for payment of sworn law enforcement representatives. In addition, the officers’ deaths must have been directly related to the injuries received from the incident."
A possible way to approach this would be to search newspaper databases at academic or large public libraries, looking for articles on the victims mentioned in the Village Voice article linked in this question. You could also try the phrase "police accidentally shot", "officer accidentally slain", etc. in Proquest or another newspaper database. You can change the search to "citation and document text", and choose the New York Times. This might give you more names of officers, so you can do further searches under those names. The next step might be JSTOR, SocIndex, Academic Search, or other large full text databases at large academic libraries, using searches such as: racism and "police departments" and "police shootings", etc.