Hundreds of American civilians are killed every year as acts of "justifiable homicide" and these deaths are avoidable. If on duty police were unable to carry firearms, far less people would be shot to death in the United States. Many other countries operate in this way and its time America demilitarizes its police force.
For example, the British manage to maintain public safety while keeping the majority of their officers unarmed.
"A 2006 survey of 47,328 Police Federation members found 82% did not want officers to be routinely armed on duty, despite almost half saying their lives had been "in serious jeopardy" during the previous three years. "
source : http://www.bbc.com/news/magazine-19641398