The soldiers in Antelope Company's Third Platoon hadn't registered a guerrilla kill in months. And without results, they feared they wouldn't be let off base for Mother's Day.

So they hatched a plan, according to Pvt. Luis Esteban Montes: Lure a civilian to their camp, murder him and register him as a rebel slain in combat.

Montes, 24, didn't object — until he met the quarry. It was Leonardo, the older brother he hadn't seen since he was 9.

Montes said he tried to dissuade his commander, who responded with threats. He slipped his brother out of the camp, he says, only to see him show up dead a week later, a "guerrilla kill" with three bullets in his torso and a gaping facial wound likely caused by a knife.

The men of Antelope Company of the 31st Rifle Batallion, 11th Brigade, 7th Division, did not get their "liberty passes." Montes' family filed a formal complaint, one of 245 complaints involving alleged killings of civilians by Colombian security forces last year that prosecutors are investigating.

It is among the most chilling examples of what the United Nations' top human rights official, Navi Pillay, calls "widespread and systematic" extrajudicial killings by Colombia's U.S.-backed military. Many of the killings were allegedly committed merely to inflate rebel casualty numbers.

Five of Montes' fellow soldiers now face a criminal probe in his brother's April 2007 death, joining some 480 soldiers under investigation for about 1,000 extrajudicial killings during the presidency of President Alvaro Uribe.

The scandal comes at a particularly delicate moment for Uribe. President-elect Barack Obama has cited human rights concerns in opposing the U.S.-Colombia trade agreement President Bush wants ratified before he leaves office in January. Obama told Bush on Tuesday that he opposes including the deal in an economic stimulus package the U.S. Congress is to begin debating next week.

Uribe, meanwhile, is cleaning house: A week before Obama's election, he ordered the biggest-ever purge of Colombia's military, firing 20 officers — including three generals and four colonels — for negligence. On election day, the army commander resigned.

Armed forces chief Gen. Freddy Padilla told The Associated Press that the Montes case contributed to the sacking of the commanding general of the 7th Division, based in Medellin. Prosecutors say there is no evidence Leonardo was a rebel — or for that matter anything more than a 33-year-old farm worker.

Montes, meanwhile, is isolated under special guard for his own safety at a military post outside Medellin.

"I can't sleep. I'm awake all night, tossing and turning in bed," he told the AP. "I have this psychosis that at any moment someone could come, something could happen to me, that they are going to kill me."

Montes told his story last month to the Colombian newsmagazine Semana. In several telephone interviews, he declined to retell the details because he is under orders not to. But he said the magazine quoted him faithfully. His testimony is also supported by declarations made to judicial authorities by Montes and others.

Here is Montes' account:

The 31st Rifles was bivouacked in the hamlet of San Juan in the northern province of Cordoba. Soldiers were listless, some malarial. Mother's Day was coming.

Montes said his batallion had a policy: "For every enemy killed you get 15 days leave." So soldiers in Montes' company began talking about "legalizing" someone — cynical service slang for killing a civilian.

One moonless rainy night, Montes' platoon leader, a corporal, told him they had chosen a victim, he said. It was a man from La Guajira, the Caribbean coastal province from which Montes himself hailed.

Curious, Montes went to see the man, gave him a cigarette and, not recognizing him in the dark, determined they were from the same town, the same street. It was Leonardo, with whom Montes shared the same father.

The two hugged and Montes, incredulous and outraged, told his brother of the sinister intentions of the soldiers who had befriended him and invited him to the camp.

Montes pleaded with the company commander, Capt. Jairo Garcia, to let him go, but said the captain told him that if he tried to stop them he would put Montes on point during patrols "so my legs could be blown off by a mine." The captain, who is under criminal investigation, called Montes a liar and a chronic slacker in a sworn declaration.

Montes got Leonardo safely out of the camp that night and figured the episode was over. But a few days later, as he was being treated for malaria in a nearby town, he learned his company had scored a "positivo" and that soldiers tried to bury his brother in an unmarked grave.

The after-action report said Leonardo was killed in a firefight with a small group of rebels. It said the others got away. Montes, citing fellow fighters, told investigators that the 9mm Browning pistol and grenade found on the body were planted by soldiers.

Montes was enraged. His brother had been killed "for nothing more than a liberty pass." The romanticized vision of soldiering Montes held when he joined the army in 2006, he says, was buried with Leonardo.

"Officers get promoted on merit and you win merit by ... killing the most subversives. But that's not so easy," Montes said. "So what happens? They look for the easiest victims."