I vehemently disagree with you. The perp came over the counter into his space, and he had no way to be assured that the perp was not going to murder or injure him. The totality of the event is horrible. One criminal died a violent death, and the shopkeeper is severely traumatized by being forced into killing another just to protect himself while backed into a corner. But that horrible set of events was put into motion by the criminal actions of those two criminals. The guy who came over the counter got a horrible outcome. But it was either him or the shopkeeper. Again, the shopkeeper has no way of assessing in that split second, that the criminal is not intending to injure or kill him.