The battle had ended and the Taliban insurgent was disarmed and seriously wounded - badly enough that one onlooker said whether he lived or died was in "Allah's hands."
But instead of arranging medical attention, Canadian Army Captain Robert Semrau fired two bullets into the insurgent's body - an act that he later described to a subordinate as a mercy killing of sorts, military prosecutors allege.
The court-martial of Capt. Semrau, 36, began in Gatineau on Wednesday. He's believed to be the first Canadian soldier to face a murder charge for an alleged battlefield killing. He pleaded not guilty.
Those who built the case against Capt. Semrau say the killing took place on Oct. 19, 2008, in the southern Afghan province of Helmand, where the Canadian officer was leading a Forces team mentoring Afghan soldiers.
In an opening statement, military prosecutors sketched out the "road map" for their case, one that uses Capt. Semrau's conversations with comrades against him.
One of these is a conversation many months later where they say Capt. Semrau confided to another Canadian Forces member that he felt bound by a "soldier's pact" to quickly end the battlefield suffering of the grievously wounded.
The army officer's lawyer, Major Steve Turner, refused to comment on the mercy-killing theory advanced by the prosecution. There's no defence in law for mercy killing.
Capt. Thomas Fitzgerald, one of the prosecutors, said some of the case details sound as if they come from the pages of a thriller penned by Frederick Forsyth or Ian Fleming: a cellphone video of the battlefield and an under-wraps mission to recover evidence from the scene of the alleged crime.
Despite all this, prosecutors must overcome the fact that they lack both a dead body and an autopsy report for the deceased, whose corpse was left behind to be buried by locals. Capt. Fitzgerald assured the judge and a panel of military jurors that these are not insurmountable obstacles.
Prosecutors say they have a witness to the shooting: An Afghan interpreter says he saw Capt. Semrau pump the second of two bullets into the unnamed insurgent's body.
Just before the incident, prosecutors say, Capt. Semrau told the interpreter and a Canadian private to leave the scene. "Turn around and … head back. You do not, or should not, have to see this," prosecutors say he said.
Moments after a "double-tap" of shots rang out, Capt. Semrau told the private that "he couldn't live with himself if he left an injured human being - and that no one should suffer like that," the prosecution said.
They say the army captain's statements to fellow soldiers should function "as admission of guilt and expressions of intention" on his part.
They paint a picture of Capt. Semrau as a warrior who believed it was acceptable to take the lives of soldiers - even foes - who had been very grievously wounded in battle.
"You do to the enemy what you would want or expect him to do to you - in keeping with this soldier's pact," the prosecution said, quoting further statements it said were made by Capt. Semrau.
Capt. Semrau's lawyer, Major Turner, said the prosecution has yet to prove its case. "The case ... at the end of the day might turn out to be very different from what they expect at this stage," he said.
The murder Capt. Semrau is alleged to have committed occurred after Afghan government forces routed a Taliban ambush, prosecutors say.
When the firefight was over, only one enemy combatant was found alive, so severely injured that it was determined his wounds couldn't be treated on the battlefield.
Afghan government forces declined to offer medical care to the man. Prosecutors said that Capt. Semrau decided the Canadians would not do so either.
The army captain is being tried under Canadian military law and is charged with second-degree murder, or alternately, attempted murder, as well as behaving in a disgraceful manner and negligence in performance of military duties.
The Forces' code of conduct, based on the International Law of Armed Conflict, says that combatants who surrender must be disarmed and that the wounded must be treated in accordance with the Geneva Convention.
The criminal charges against Capt. Semrau are the most serious a Canadian soldier has faced since Somalia in the 1990s, when Master Corporal Clayton Matchee beat a Somali teenager to death.
The prosecution is expected to present its case before the defence in the Semrau court martial. In a military trial, a jury is replaced by a panel of five enlisted soldiers, who in this case are all officers ranging from a naval commodore to a captain. They decide questions of fact.