that isn't a legal requirement to reach a "terrorist" status.
I'm not sure there is an agreed upon legal definition of, "terrorist". Although, Enemy Combatant comes to mind.
But, as I understand it, the charge is the use of a weapon of mass destruction. That's got to count for something.
(a)
Offense Against a National of the United States or Within the United States.— A person who, without lawful authority, uses, threatens, or attempts or conspires to use, a weapon of mass destruction— (1) against a national of the United States while such national is outside of the United States;
(2) against any person or property within the United States, and (A) the mail or any facility of interstate or foreign commerce is used in furtherance of the offense;
(B) such property is used in interstate or foreign commerce or in an activity that affects interstate or foreign commerce;
(C) any perpetrator travels in or causes another to travel in interstate or foreign commerce in furtherance of the offense; or
(D) the offense, or the results of the offense, affect interstate or foreign commerce, or, in the case of a threat, attempt, or conspiracy, would have affected interstate or foreign commerce;
(3) against any property that is owned, leased or used by the United States or by any department or agency of the United States, whether the property is within or outside of the United States; or
(4) against any property within the United States that is owned, leased, or used by a foreign government,
shall be imprisoned for any term of years or for life, and if death results, shall be punished by death or imprisoned for any term of years or for life.
Edit:
18 USC § 2332a - Use of weapons of mass destruction