[Post removed; there are other forms of illegal transactions, so don't speculate on what crime was committed. If you witnessed the transaction, you should contact the police department.]

Doesn't matter whether the transaction is legal or not. Someone got upset and escalated the conflict with a gun. Even people who sell items without paying sales tax or fail to report payments to babysitters should be protected from gun violence. Classifying tax cheats and drug users as lower class citizens diminishes us all. Focus should be on getting the shooter off the street.