Related Rule
United States of America
Practice Relating to Rule 107. Spies
Section B. Status of spies
The US Field Manual (1956) provides: “In addition to the ‘grave breaches’ of the Geneva Conventions of 1949, the following acts are representative of violations of the law of war (‘war crimes’): … killing without trial spies”. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 504(l).
With respect to occupied territories, the manual uses the same wording as Articles 5 of the 1949 Geneva Convention IV. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 248.
The US Air Force Pamphlet (1976) states: “Protected persons in occupied territory who are detained for spying … are guaranteed the right to a fair trial.” 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 14-2.
The US Air Force Commander’s Handbook (1980) provides: “Even … spies … have the right to be tried and cannot be summarily executed.” 
United States, Air Force Pamphlet 110-34, Commander’s Handbook on the Law of Armed Conflict, Judge Advocate General, US Department of the Air Force, 25 July 1980, § 4-2(e).
The US Instructor’s Guide (1985) states: “In addition to the grave breaches of the 1949 Geneva Conventions, the following acts are further examples of war crimes: … killing, without proper legal trial, spies”. 
United States, Instructor’s Guide – The Law of War, Headquarters Department of the Army, Washington, April 1985, pp. 13 and 14.
The US Naval Handbook (1995) states:
Spying during armed conflict is not a violation of international law. Captured spies are not, however, entitled to prisoner-of-war status. The captor nation may try and punish spies in accordance with its national law. Should a spy succeed in eluding capture and return to friendly territory, liability to punishment terminates. If subsequently captured during some other military operation, the former spy cannot be tried or punished for the earlier act of espionage. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 12.8.1.
The Handbook specifies that “individuals captured as spies … may not be summarily executed” and that they “have the right to be fairly tried for violations of the law of armed conflict”. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 11.7.
The US Manual for Military Commissions (2007), Part IV, Crimes and Elements, includes in the list of crimes triable by military commissions:
SPYING.
a. Text. “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 power, collects or attempts to collect information by clandestine means or while acting under false pretenses, for the purpose of conveying such information to an enemy of the United States, or one of the co-belligerents of the enemy, shall be punished by death or such other punishment as a military commission under this chapter may direct.”
b. Elements.
(1) The accused collected or attempted to collect certain information by clandestine means or while acting under false pretenses;
(2) The accused intended or had reason to believe the information collected would be used to injure the United States or to provide an advantage to a foreign power;
(3) The accused intended to convey such information to an enemy of the United States or one of the co-belligerents of the enemy; and
(4) The conduct took place in the context of and was associated with armed conflict.
c. Maximum punishment. Death. 
United States, Manual for Military Commissions, published in implementation of the Military Commissions Act of 2006, 10 U.S.C. §§ 948a, et seq., 18 January 2007, Part IV, § 6(27), p. IV-20.
The US Naval Handbook (2007) states:
Spying during armed conflict is not a violation of international law. Captured spies are not, however, entitled to prisoner-of-war status. The captor nation may try and punish spies in accordance with its national law. Should a spy succeed in eluding capture and return to friendly territory, he is immune from punishment for his past espionage activities. If subsequently captured during some other military operation, the former spy cannot be tried or punished for the earlier act of espionage. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Homeland Security, US Coast Guard, July 2007, § 12.9.
The US Manual for Military Commissions (2010), Part IV, Crimes and Elements, includes in the list of crimes triable by military commissions:
SPYING.
a. Text. “Any person subject to this chapter who, in violation of the law of war and 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 power, collects or attempts to collect information by clandestine means or while acting under false pretenses, for the purpose of conveying such information to an enemy of the United States, or one of the co-belligerents of the enemy, shall be punished by death or such other punishment as a military commission under this chapter may direct.”
b. Elements.
(1) The accused collected or attempted to collect certain information by clandestine means or while acting under false pretenses;
(2) The accused intended or had reason to believe the information collected would be used to injure the United States or to provide an advantage to a foreign power;
(3) The accused intended to convey such information to an enemy of the United States or one of the co-belligerents of the enemy;
(4) The conduct was in violation of the law of war; and
(5) The conduct took place in the context of and was associated with hostilities.
c. Comment. For purposes of offenses (13) [intentionally causing serious bodily injury], (15) [murder in violation of the law of war], (16) [destruction of property in violation of the law of war], and (27) [spying] in Part IV of this Manual (corresponding to offenses enumerated in paragraphs (13), (15), (16), and (27) of § 950t of title 10, United States Code), an accused may be convicted in a military commission for these offenses if the commission finds that the accused employed a means (e.g., poison gas) or method (e.g., perfidy) prohibited by the law of war; intentionally attacked a “protected person” or “protected property” under the law of war; or engaged in conduct traditionally triable by military commission (e.g., spying; murder committed while the accused did not meet the requirements of privileged belligerency) even if such conduct does not violate the international law of war.
d. Maximum punishment. Death. 
United States, Manual for Military Commissions, published in implementation of Chapter 47A of Title 10, United States Code, as amended by the Military Commissions Act of 2009, 10 U.S.C, §§ 948a, et seq., 27 April 2010, § 5(27), pp. IV-21 and IV-22.
The US Military Commissions Act (2006), passed by Congress following the Supreme Court’s decision in Hamdan v. Rumsfeld in 2006, amends Title 10 of the United States Code and, inter alia, provides the penalty for “spying”: “Any person subject to this chapter who [commits the offense of spying] … shall be punished by death or such other punishment as a military commission under this chapter may direct.” 
United States, Military Commissions Act, 2006, Public Law 109-366, Chapter 47A of Title 10 of the United States Code, 17 October 2006, p. 120 Stat. 2630, § 950v(b)(27).
The US Military Commissions Act (2009) amends Chapter 47A of Title 10 of the United States Code as follows:
§ 950t. Crimes triable by military commission
“The following offenses shall be triable by military commission under this chapter at any time without limitation:
“(27) SPYING.—Any person subject to this chapter who, in violation of the law of war and 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 power, collects or attempts to collect information by clandestine means or while acting under false pretenses, for the purpose of conveying such information to an enemy of the United States, or one of the co-belligerents of the enemy, shall be punished by death or such other punishment as a military commission under this chapter may direct. 
United States, Military Commissions Act, 2009, § 950t(27).
In the Dostler case before the US Military Commission at Rome in 1945, the accused, the commander of a German army corps, was found guilty of having ordered the shooting of 15 American prisoners of war in violation of the 1907 Hague Regulations and of long-established laws and customs of war. The Defence submitted that the US soldiers had worn no distinctive emblem and that their mission had been undertaken for the purpose of sabotage. The Defence considered, therefore, that they were not entitled to the privileges of a lawful belligerent, though it was admitted that they were entitled to a lawful trial even if they were treated as spies. 
United States, Military Commission at Rome, Dostler case, Judgment, 12 October 1945.
In 2008, in the Khadr case, a Guantánamo Military Commission considered a Defence motion to dismiss a charge of murder brought against the defendant, which was defined as follows:
CHARGE I: VIOLATION OF 10 U.S.C. §950v(b)(15), MURDER IN VIOLATION OF THE LAW OF WAR
Specification: In that [the defendant], a person subject to trial by military commission as an alien unlawful enemy combatant, did, in Afghanistan, on or about July 27, 2002, while in the context of and associated with armed conflict and without enjoying combatant immunity, unlawfully and intentionally murder [a] U.S. Army Sergeant First Class … , in violation of the law of war, by throwing a hand grenade at U.S. forces resulting in the death of [the] Sergeant First Class. 
United States, Guantánamo Military Commission, Khadr case, Ruling, 21 April 2008, § 2.
The Commission stated the following in relation to the lawfulness of the offence of murder being tried by US military commissions:
As if anticipating the defense motion in this case, the Supreme Court actually defined those who are protected by the Law of Nations and those who are not:
By universal agreement and practice the law of war draws a distinction between the armed forces and the peaceful populations of belligerent nations and also between those who are lawful and unlawful combatants … Unlawful combatants are likewise subject to capture and detention, but in addition they are subject to trial and punishment by military tribunals for acts which render their belligerency unlawful. The spy who secretly and without uniform passes the military lines of a belligerent in time of war, seeking to gather military information and communicate it to the enemy … [is a familiar example of a belligerent who is] generally deemed not to be entitled to the status of prisoners of war, but to be … [an offender] against the law of war subject to trial and punishment by military tribunals. (Ex Parte Quirin, Id., at 12, emphasis added). 
United States, Guantánamo Military Commission, Khadr case, Ruling, 21 April 2008, § 6.
[emphasis in original]