Balko determines that 2012 "is on pace to be the safest ever for America's police officers":
According to the FBI's Uniform Crime Reports, the homicide rate for police officers in 2010 (the last year for which data is available) was about 7.9 per 100,000 officers. That's about 60 percent higher than the overall homicide rate in America, which is 4.8. But it's lower than the homicide rates in many large cities, including Atlanta (17.3), Boston (11.3), Dallas (11.3), Kansas City (21.1), Nashville (8.9), Pittsburgh (17.3), St. Louis (40.5), or Tulsa (13.7).
In fact, of the 74 U.S. cities with populations of 250,000 or more, 36 have murder rates higher than that of police in America. It's more likely to be murdered just by living in these cities than the average police officer is to be murdered on the job.
The job of police officer also isn't anywhere near the most dangerous job in America. If we include traffic fatalities, the job of police officer will in some years rank among the 10 most dangerous in America (PDF). But take away car accidents, and it doesn't come close.