be helpful in case of self-defense. right after that we saw prosecutors saw it could be used in case of murder. >> let's talk about one of the george zimmerman's former college professors. there were a couple that took the stand. alexis carter testified zimmerman got an a in his criminal justice class and he also taught the stand your ground law. what was the significance of letting the jurors know he was very much aware of that type of law. >> reporter: specifically the stand your ground law. carter made the point in his class it was practical application. he showed his students video of what to do in different se fan e owes. it was a point that don west learned about this and this is not textbook explanation. it's more practical application of what to do in different scenarios and clearly it goes to