The requirements may vary from state to state on this one.

Assume the following scenario: You're in a parking garage and a thug approaches and attempts to mug you. Hearing his threat and seeing he has a large knife, you're able to draw your weapon. At this point the thug drops the knife and runs away obviously realizing he's made a serious underestimation of his target.

What are your legal responsibilities at this point for:
1) NOT being reported as an individual brandishing a firearm
2) What do you do about the large knife now unclaimed on the ground
3) Obviously this area is not one you consider safe. If you leave immediately are there any ramifications from the incident?