Agreed that the burglars were low-lives and absolutely in the wrong. No question about that. And perhaps the shock of the situation and the adrenaline running through the old man's body made him think less rationally than he should have and that should be taken into account.
HOWEVER, since this IS a pro-life site, where abortion is considered murder of an innocent child (which is what it is), let's play "what if" for a moment (assuming this woman was being truthful her pregnancy). If this woman committed a burglary with a baby in her arms (which has occurred many times), ran away, fell, got cornered by the man and said: "Don't shoot, I'm holding a baby," and he shot her anyway, I assume we there would be less sympathy for the older man.
In any event the woman was a criminal to break into a man's home and rob him. But does that lessen the fact that he knowingly killed a pregnant woman, which we pro-lifers agree are two humans temporarily sharing one body? If it went down as reported, the woman was a thief, but the old man is a murderer.