These are the general articles regarding murder under the Uniform Code of Military Justice. These are laws that are in effect in the absense of War. However, we are still engaged in a declaration of WAR, so these might be different.
http://www.army.mil/references/UCMJ/ucmj2.html#918. ART. 118. MURDER
918. ART. 118. MURDER Any person subject to this chapter whom without justification or excuse, unlawfully kills a human being, when he- – (1) has a premeditated design to kill; (2) intends to kill or inflict great bodily harm; (3) is engaged in an act which is inherently dangerous to others and evinces a wanton disregard of human life; or (4) is engaged in the perpetration or attempted perpetration of burglary, sodomy, rape, robbery, or aggravated arson; is guilty of murder, and shall suffer such punishment as a court-martial may direct, except that if found guilty under clause (1) or (4), he shall suffer death or imprisonment for life as a court-martial may direct.
(c) Any person found guilty of desertion or attempt to desert shall be punished, if the offense is committed in time of war, by death or such other punishment as a court-martial may direct, but if the desertion or attempt to desert occurs at any other time, by such punishment, other than death, as a court-martial may direct.
Any person subject to this chapter who–
(1) strikes his superior commissioned officer or draws or lifts up any weapon or offers any violence against him while he is in the execution of his officer; or
(2) willfully disobeys a lawful command of his superior commissioned officer;
shall be punished, if the offense is committed in time of war, by death or such other punishment as a court-martial may direct, and if the offense is committed at any other time, by such punishment, other than death, as a court-martial may direct.
Any person subject to this chapter who in time of war discloses the parole or countersign to any person not entitled to receive it or who gives to another who is entitled to receive and use the parole or countersign a different parole or countersign from that which, to his knowledge, he was authorized and required to give, shall be punished by death or such other punishment as a court- martial may direct.
Could he be considered aiding the enemy?
Any person who–
(1) aids, or attempts to aid, the enemy with arms, ammunition, supplies, money, or other things; or
(2) without proper authority, knowingly harbors or [protects or gives intelligence to or communicates or corresponds with or holds any intercourse with the enemy, either directly or indirectly;
shall suffer death or such other punishment as a court-martial or military commission may direct.
Could he be considered a spy:
Any person who in time of war is found lurking as a spy or acting as a spy in or about any place, vessel, or aircraft, within the control or jurisdiction of any of the armed forces, or in or about any shipyard, any manufacturing or industrial plant, or any other place or institution engaged in work in aid of the prosecution of the war by the Unites States, or elsewhere, shall be tried by a general court-martial or by a military commission and on conviction shall be punished by death.
(A) (1) Any person subject to this chapter who, with intent or reason to believe that it is to be used to the injury of the United States or to the advantage of a foreign nation, communicates, delivers, or transmits, or attempts to communicate, deliver, or transmit, to any entity described in paragraph (2), either directly or indirectly, any thing described in paragraph (3) shall be punished as a court-martial may direct, except that if the accused is found guilty of an offense that directly concerns (A) nuclear weaponry, military spacecraft or satellites, early warning systems, or other means of defense or retaliation against large scale attack, (B) war plans, (C) communications intelligence or cryptographic information, or (D) any other major weapons system or major element of defense strategy, the accused shall be punished by death or such other punishment as a court- martial may direct.
(2) An entity referred to in paragraph (1) is–
(A) a foreign government;
(B) a faction or party or military force within a foreign country, whether recognized or unrecognized by the United States
(C) a representative, officer, agent, employee, subject, or citizen of such government, faction, party, or force.
(3) A thing refereed to in paragraph (1) is a document, writing, code book, signal book, sketch, photograph, photographic negative, blueprint, plan, map, model, note, instrument, appliance or information relating to the national defense.
(b) (1) No person may be sentenced by court-martial to suffer death for an offense under this section (article) unless–
(A) the members of the court-martial unanimously find at least one of the aggravating factors set out in subsection (c); and
(B) the members unanimously determine that any extenuating or mitigating circumstances are substantially outweighed by any aggravating circumstances, including the aggravating factors set out under subsection (c).
(2) Findings under this subsection may be based on–
(A) evidence introduced on the issue of guilt or innocence;
(B) evidence introduced during the sentencing proceeding; or
(C) all such evidence.
(3) The accused shall be given broad latitude to present matters in extenuation and mitigation.
(c) A sentence of death may be adjudged by a court-martial for an offense under this section (article) only if the members unanimously find, beyond a reasonable doubt, one or more of the following aggravating factors:
(1) The accused has been convicted of another offense involving espionage or treason for which either a sentence of death or imprisonment for life was authorized by statute.
(2) In the commission of the offense, the accused knowingly created a grave risk of substantial damage to the national security.
(3) In the commission of the offense, the accused knowingly created a grave risk of death to another person.
(4) Any other factor that may be prescribed by the President by regulations under section 836 of this title (Article 36).
Any person subject to this chapter who, with intent to deceive, signs any false record, return, regulation, order, or other official document, knowing it to be false, or makes any other false official statement knowing it to be false, shall be punished as a court-martial may direct.