Police are not trained to kill.
In most cases they are not even trained to handle a firearm safely, properly, and therefore accurately.
The average hit rate during gunfights is just 18 percent. When suspects are un-armed or otherwise do not return fire, police officers hit their targets only 30 percent of the time.
In a crowded situation they are more likely to hit innocent bystanders than the suspect.
On Saturday night in New York City’s Times Square, police opened fire on a man who was walking erratically into oncoming traffic and, when approached by law enforcement, reached into his pocket as if he were grabbing a weapon. The officers fired three shots. One hit a 54-year-old woman in the knee and another grazed a 35-year-old woman’s buttocks. None hit the suspect, whom police subsequently subdued with a taser.
While incidents of police shooting bystanders are uncommon, they shouldn’t surprise New Yorkers (or anyone else) when they happen. Just last year, New York police injured nine onlookers in the course of responding to a murder suspect near the Empire State Building. As police chased the man through rush hour crowds, he fired at the cops; they returned 16 shots, hitting the man 10 times. That actually counted as accurate shooting for the NYPD.
http://nation.time.com/2013/09/16/ready-fire-aim-the-science-behind-police-shooting-bystanders/