Chase the driver. Stopping for the injured isn't going to help them much - either they'll die immediately or not at all. A few weeks ago I saw a hit and run, but it was car on car. Couldn't believe it. But I got the plate number and gave it to the lady and cop afterwards. Wish I knew if they caught the d*ckhead. And there were 3 three of us standing on the sidewalk right next to where it happened.
Note to self (if you're a d*ckhead): Don't run when witnesses abound.