Another thing you could do if you worked there would be to:
Pour a lot of gasoline inside of a room that can be locked
At gunpoint, throw the other employees into the room and lock it
When more people come into the store, do the same to them
Unlock the door, throw some flaming matches in the room, and lock the door again
Take the surveillance tapes
Use a gasoline pump to spray gasoline all over the building and the gasoline pumps
Throw another burning match when you are at a safe distance.
If anyone questions you... Blame the statue that got your evil twin high, while he was playing guitar, with his fingertips, while in a spacesuit.