Maybe I should be in jail. Not long ago, a squirrel ran under the car while I was driving with my two daughters. In the mirror, I could see it flopping around. I backed up and ran over it again. (But just once.)
The girls were appalled till they had time to think about it. No way were we going to pay for a vet for the squirrel, so the alternative was to allow it to suffer till it died.
Based on most of the comments (at least the comments of the animal lovers) on this thread, I guess the appropriate response would have been to drive away and let it suffer.