... from 1980–2014, an average of 64 law enforcement officers have been feloniously killed per year. The 2013 total, 27, was the lowest during this 35-year period. Last year there were 51.

I can't find statistics for this year that specify cause of death, and since a large majority of officers who die in the line of duty die of traffic accidents, the numbers I could find are less than useful.

Generally, these numbers don't appear to be going up. If anything, they've decreased - which may have more to do with police officers wearing more and better protective equipment than anything else.