According to his testimony, the perps looked at each other, and one started over his lawn toward him. When he shouldered his shotgun, the perps both broke and ran instead. He shot three times and killed both men, after a long pause audible on the (unbroken) 911 call. The men turned out to be unemployed illegal Columbian immigrants, with prior felony convictions, as well as $2,000-ish in loot from Horn's neighbor's house.
Horn's case was put before a grand jury, who were given all the particulars of the case, and after deliberation refused to indict Horn. Horn's defense cited the Castle Doctrine, which is a Texas law permitting use of deadly force in defense of home and property; this was probably not applicable, strictly speaking, in Horn's case as defense of a neighbor's property is only covered with the neighbor's permission, which it is unclear that Horn had. Without this explicit permission, the grand jury's refusal to indict is an example of jury nullification, itself a hot topic all over the country as, apparently, very few American citizens understand the concept anymore.
Counter-example: also in Texas, one month ago, a different old man shot out his front window and killed an "intruder" who turned out to be a 15 year old neighbor crossing his yard with a friend. This case was also brought before a grand jury, and that grand jury promptly indicted that old man for murder.
Question: why is this "broken", and how would "fixing" it make society any "better"?
You show me a case where the old man who shoots through the window without warning and kills a neighbor doesn't get indicted, and I will promptly get outraged as fuck. But you're going to have difficulty finding a case like that to show me. In the meantime, I'm not too worried about Joe Horn - yes, he needed to be brought before a grand jury; but yes, he also probably deserved for them to refuse to indict.