I was trying to stay away from issues of scale, which is what the last statement brought in, as well as the second to last, though to a lesser degree.

The problem with elements of degree is that by your definition, a single suicide bomber with a bomb belt, who walks into a department store and detonates the bomb wouldn't count as a terrorist because his death toll wasn't high enough. Surely that is not correct.

Furthermore, both the DC Snipers and Mr. Anthrax actually managed far more "terror" because they were prolonged. 9/11 is a closer match to VATech in that it was a nearly instantaneous event, though the death toll was much higher.

I would say that it is still terrorism if it happens over a long time period instead of an instant, and it is still terrorism if the deathtoll is pretty low (Mr. Anthrax killed a very small number of people, but had a HUGE financial and psychological impact).

This leaves the first statements. Is terrorism only terrorism if the person/persons are acting as agents for a known organization? What if the organization denies the involvement, but the attacker still claims to have acted in their behalf?

After all, by that definition, neither McVeigh, nor the Unabomber were actually terrorists, even though their techniques and methods appeared similar to other terrorist acts, because they were acting alone, and without ties to any organization. That's fine, but what about Eric Rudolph? He was the Atlanta Olympics bomber, and had bombed a few other places. He had ties to organizations, but the organizations denied that he represented them. While this might be true, it leaves the question of whether he was a terrorist.

Consider that if two people detonate bomb belts on busses in Israel. One of them is a member of a known organization, such as Hamas. The other was just pissed about Israelly occupation of Gaza, or even Starbucks. Is the second one not a terrorist simply because he didn't belong to a group? That doesn't sound right to me.