American police aren't trained to "shoot to kill." They are trained to shoot to stop the threat. The most reliable way to stop a deadly threat is to shoot at the body mass, which sometimes results in death.
Of course, it's preferable to deescalate the situation and use better judgment when in a confrontation to avoid shooting at all.
They aren't trained to shoot to kill per se, but by aiming at the center mass the end result is many so called threats ending up in body bags and very few on a gurney going to the hospital. Also how often does a cop stop shooting after one shot? When you are shot six or more times in the center mass, the end result is usually death.