Does anyone know if it would have been legal for an armed citizen to fire at the truck as it got away?
Yes...if they were a direct witness, and could prove to a reasonable person that letting the subject go would be more dangerous than letting him go.
Basically, you better witness someone on a rampage or killing a cop (or agent of the government as in this case) before you take things into your own hands.
SOURCE: ACA 5-2-607.Use of deadly physical force in defense of a person.
(a)A person is justified in using deadly physical force upon another person if the person reasonably believes that the other person is:
(1)Committing or about to commit a felony involving force or violence;
(2)Using or about to use unlawful deadly physical force; or
(3)(A)Imminently endangering the person's life or imminently about to victimize the person as described in § 9-15-103 from the continuation of a pattern of domestic abuse.
(B)As used in this section, “domestic abuse” means the same as defined in § 9-15-103.
(b)A person may not use deadly physical force in self-defense if he or she knows that he or she can avoid the necessity of using deadly physical force with complete safety:
(1)(A)By retreating.
(B)However, a person is not required to retreat if the person is:
(i)In the person's dwelling or on the curtilage surrounding the person's dwelling and was not the original aggressor; or
(ii)A law enforcement officer or a person assisting at the direction of a law enforcement officer; or
(2)By surrendering possession of property to a person claiming a lawful right to possession of the property.
(c)As used in this section, “curtilage” means the land adjoining a dwelling that is convenient for family purposes and habitually used for family purposes, but not necessarily enclosed, and includes an outbuilding that is directly and intimately connected with the dwelling and in close proximity to the dwelling.
History.Acts 1975, No. 280, § 507; A.S.A. 1947, § 41-507; Acts 1997, No. 1257, § 1; 2007, No. 111, § 1.
As I understand it, one is not supposed to fire unless it is to protect his own life, or the life of another person who is immediately threatened.
You pretty much need to be returning fire while it is an ongoing incident, in order to prove that you were in immediate danger and fear for your life.....