Well the cops obviously weren’t there in the store to see it first hand. And they obviously came to the store after being called about something. It is a safe deduction from those facts that they came to the store after being told something was happening in the store by the Costco clerk who called 911. Ergo the clerk was the source of their description.
And armed man damaging store property. So what in that justified the police overreaction? Or are you honestly trying to convice us that the only parties in all this more innocent than the dead guy are the men who shot him?