Domestic Terrorism For Thee, But Not For Dr. Tiller's Assassin

Why is throwing two ground burst simulators (practice grenades) into a crowd of strangers in a parking lot considered domestic terrorism, but shooting someone in the head, someone you've explicitly targeted for terrorism, not so much?

I thought maybe it's because soldiers are held to a higher standard of conduct than civilians but, since the charges were brought by civilian authorities, I don't see how you can make an argument that some people deserve to be held to a different standard under the law just because of their chosen profession. Very odd, indeed.