You have to love Texas:

In the same article linked by the OP, he is justified..............

"...."I can point you exactly where it is in the law, 9.31 and 9.32 of the penal code," said Nathan Beedle with the Harris County District Attorney's Office.

Beedle says Texas law outlines specific instances pertaining to robbery by threat, or aggravated robbery, where deadly force is presumed justified.

"Whether someone uses deadly force in the situation, that is presumed to be correct under Texas law," Beedle said. ........"