Actually, gun violence has been on a downward trend since the early nineties across the entire population. You'd expect police firearm fatalities to trend downward accordingly, regardless of the use of body armor.
Police wearing body armor, armored cars, AR-15s, and the like are part of a different trend: the militarization of US police using surplus equipment from the Department of Defense, in a DOD program 1033.
It's interesting to combine that with traffic stop data to get an idea of how risky it is for a person who is pulled over.
There are at least 17.7 million people pulled over for traffic stops per year in the US. If we attribute ALL of the deaths to traffic stops to get an upper bound of 3.5 deaths per 100k for people in traffic stops per year.
That puts the probability of getting killed during a traffic stop in a given year at about the same as the probability of dying that year from stomach cancer. It's about half the probability of dying by suicide from firearm, and 3 times the probability of dying by influenza.
That's a very generous upper bound. Only 2% of the descriptions at Wikipedia mention traffic, but that is too low because some do not have descriptions. Let's be generous and go with 10% to get a more realistic bound than the 100% I used earlier. That would give a death rate from traffic stops of 0.35 per 100k.
That would put the probability of dying when you are pulled over as similar to the probability of dying that year from Hodgkin's disease, and about 1/3 the probability of dying from malnutrition [1].
[1] malnutrition deaths are way higher than I would have expected in the US!
It's worth reading through at least some of the particulars. About half seem to involve people also shooting at the police. Assuming the police are at fault every other time, I don't know how else one would expect a shootout with police to end. For that matter, even if it happens to be a fake gun, waving it around and refusing to put it down is probably a bad idea.
And then there's murder suicides by people who happen to be cops, but I don't think killing your own family is something that comes up in the line of duty.
This number is trending downwards since in the mid-seventies.
http://www.nbcnews.com/news/crime-courts/u-s-police-officer-...