This one is easy!


http://www.capitol.state.tx.us/tlodocs/80R/billtext/html/SB00378F.htm
Here's a couple of quotes from the actual law:
Here's the places where someone can use lethal force:
You can protect yourself in all cases on your property, OR protect others in cases of protecting another person from a crime against their person... NOT the other person's property.
You're right that it is easy, but wrong about the law. The right to use deadly force already existed under Texas law before the new law went into effect in September. The existing law clearly states he can use deadly force to prevent the crime of burglary or trespassing at night, even if he is doing so to protect a third party's property. The answer IS easy, he has an affirmative defense to prosecution in that he acted lawfully to protect the property of his neighbor. My guess is the grand jury will probably not even indict him.
But as Bikewer pointed out, he probably will get sued in civil court. And also as Bikewer correctly notes, law enforcement officers, even in Texas, are held to the US Supreme Court's definition of the use of deadly force as a seizure under the 4th Amendment. That means a peace officer in Texas CANNOT shoot someone just for burglarizing a building at night, but the average citizen can.
§ 9.02. JUSTIFICATION AS A DEFENSE. It is a defense toprosecution that the conduct in question is justified under this chapter.
§ 9.41. PROTECTION OF ONE'S OWN PROPERTY. (a) A person in lawful possession of land or tangible, movable property is justified in using force against another when and to the degree the actor reasonably believes the force is immediately necessary to prevent or terminate the other's trespass on the land or unlawful interference with the property.
(b) A person unlawfully dispossessed of land or tangible, movable property by another is justified in using force against the other when and to the degree the actor reasonably believes the force is immediately necessary to reenter the land or recover the property if the actor uses the force immediately or in fresh pursuit after the dispossession and:
(1) the actor reasonably believes the other had no claim of right when he dispossessed the actor; or (2) the other accomplished the dispossession by using force, threat, or fraud against the actor.
Acts 1973, 63rd Leg., p. 883, ch. 399, § 1, eff. Jan. 1, 1974. Amended by Acts 1993, 73rd Leg., ch. 900, § 1.01, eff. Sept. 1, 1994.
§ 9.42. DEADLY FORCE TO PROTECT PROPERTY. A person is justified in using deadly force against another to protect land or tangible, movable property:
(1) if he would be justified in using force against the other under Section 9.41; and (2) when and to the degree he reasonably believes the deadly force is immediately necessary:
(A) to prevent the other's imminent commission of arson, burglary, robbery, aggravated robbery, theft during the nighttime, or criminal mischief during the nighttime; or
(B) to prevent the other who is fleeing immediately after committing burglary, robbery, aggravated robbery, or theft during the nighttime from escaping with the property; and
(3) he reasonably believes that:
(A) the land or property cannot be protected or recovered by any other means; or
(B) the use of force other than deadly force toprotect or recover the land or property would expose the actor oranother to a substantial risk of death or serious bodily injury.
Acts 1973, 63rd Leg., p. 883, ch. 399, § 1, eff. Jan. 1, 1974. Amended by Acts 1993, 73rd Leg., ch. 900, § 1.01, eff. Sept. 1, 1994.