OK, I have stayed out of this so far, but here is my 2¢.
When shooting in self defense, your allowed to stop the threat. In this case, if the threat was no longer there, and he continued to attack (after a reasonable period that allowed him to asses the threats existence), then he is wrong and guilty of murder. If they can prove the guy on the floor was still a threat and he had no recourse but to fire again, then he should be acquitted.
Oklahoma does not have a Castle Doctrine, but is a Stand Your Ground state. Here is their statute:
Oklahoma Statutes Citationized
§21-1289.25
--------------------------------------------------------------------------------
A. The Legislature hereby recognizes that the citizens of the State of Oklahoma have a right to expect absolute safety within their own homes.
B. A person is presumed to have held a reasonable fear of imminent peril of death or great bodily harm to himself or herself or another when using defensive force that is intended or likely to cause death or great bodily harm to another if:
1. The person against whom the defensive force was used was in the process of unlawfully and forcefully entering, or had unlawfully and forcibly entered, a dwelling, residence, or occupied vehicle, or if that person had removed or was attempting to remove another against the will of that person from the dwelling, residence, or occupied vehicle; and
2. The person who uses defensive force knew or had reason to believe that an unlawful and forcible entry or unlawful and forcible act was occurring or had occurred.
C. The presumption set forth in subsection B of this section does not apply if:
1. The person against whom the defensive force is used has the right to be in or is a lawful resident of the dwelling, residence, or vehicle, such as an owner, lessee, or titleholder, and there is not a protective order from domestic violence in effect or a written pretrial supervision order of no contact against that person;
2. The person or persons sought to be removed are children or grandchildren, or are otherwise in the lawful custody or under the lawful guardianship of, the person against whom the defensive force is used; or
3. The person who uses defensive force is engaged in an unlawful activity or is using the dwelling, residence, or occupied vehicle to further an unlawful activity.
D. A person who is not engaged in an unlawful activity and who is attacked in any other place where he or she has a right to be has no duty to retreat and has the right to stand his or her ground and meet force with force, including deadly force, if he or she reasonably believes it is necessary to do so to prevent death or great bodily harm to himself or herself or another or to prevent the commission of a forcible felony.
E. A person who unlawfully and by force enters or attempts to enter the dwelling, residence, or occupied vehicle of another person is presumed to be doing so with the intent to commit an unlawful act involving force or violence.
F. A person who uses force, as permitted pursuant to the provisions of subsections B and D of this section, is justified in using such force and is immune from criminal prosecution and civil action for the use of such force. As used in this subsection, the term "criminal prosecution" includes charging or prosecuting the defendant.
G. A law enforcement agency may use standard procedures for investigating the use of force, but the law enforcement agency may not arrest the person for using force unless it determines that there is probable cause that the force that was used was unlawful.
H. The court shall award reasonable attorney fees, court costs, compensation for loss of income, and all expenses incurred by the defendant in defense of any civil action brought by a plaintiff if the court finds that the defendant is immune from prosecution as provided in subsection F of this section.
I. The provisions of this section and the provisions of the Oklahoma Self-Defense Act, Sections 1290.1 through 1290.26 of this title, shall not be construed to require any person using a pistol pursuant to the provisions of this section to be licensed in any manner.
J. As used in this section:
1. "Dwelling" means a building or conveyance of any kind, including any attached porch, whether the building or conveyance is temporary or permanent, mobile or immobile, which has a roof over it, including a tent, and is designed to be occupied by people;
2. "Residence" means a dwelling in which a person resides either temporarily or permanently or is visiting as an invited guest; and
3. "Vehicle" means a conveyance of any kind, whether or not motorized, which is designed to transport people or property.
It is now going to be up to courts to sort out if he should stand trial and the defense attorney to get him off. Section D above is IMO what the defense attorney will have to prove to let this be deemed a good shoot.