He didn't escalate. Deadly force threshold had been crossed. He met force with force.
That was my thinking too. How do you 'escalate' beyond deadly force? The Nuclear option??
The real issue is protecting the companies ass. They do not want to be party to a lawsuit if an innocent (or not so innocent) person in the store accidentally catches a slug from an employee's gun.
So they'll let their pharmacists be fish in a bowl for these scumbag hoods.