I guess those he killed and took hostage just didn’t understand the duty to retreat consensus - if they had all been armed, the perp would have died a lot quicker and a few more of the victims would be alive.
That is why in some states it is legal to shoot arsonists. So many of these events seem to start with the bad guy starting a fire at his home.
Texas Penal Code - Section 9.42
“A) to prevent the other’s imminent commission of
arson, burglary
...
B) the use of force other than deadly force to
protect or recover the land or property would expose the actor or
another to a substantial risk of death or serious bodily injury.”