Here's the law on the Multistate Bar Exam - The use of deadly force is NEVER allowed to protect property and may only be used if to PREVENT the commission of a VIOLENT FELONY, such as burglary.
Under the MBE, this is a classic case of murder reduced to manslaughter by reason of exciting event with insufficient time to cool off. Horn used deadly force AFTER the crime had been committed so the prevention element is missing. Also, it wasn't a violent felony because burglary is the unlawful entry of a dwelling with the intent to commit a felony AT NIGHT. This happened in broad daylight. http://www.telegraph.co.uk/news/worldnews/1571085/Texan-%27hero%27-shoots-and-kills-burglars.html they have more than probable cause to arrest Horn right now.
I didn't really read whatever else was said in this thread, but I disagree that this is a "classic case" of insufficient time to cool off.
Voluntary manslaughter isn't usually available unless there is a bar fight or another guy screwing your wife.
After reading the Tx. penal code, it looks like they (like most jurisdictions) have eliminated the nighttime requirement for burglary. Remember, the MBE tests mostly on common law, most of which has been abrogated by statute by the state legislatures.
Arguing that burglary, whenever it occurs, is not a dangerous felony is just absurd. It's an enumerated "inherently dangerous" felony in all felony murder statutes. There's a reason for that.