WASHINGTON — Army Staff Sgt. Robert Bales initially asserted that he had shot several Afghan men outside a U.S. combat outpost in southern Afghanistan on March 11 and did not mention that a dozen women and children were among the dead, according to a senior U.S. official briefed on the case.

“He indicated to his buddies that he had taken out some military-aged males,” the senior official said. Soldiers normally use that term to denote insurgents.

But Bales’ story soon broke down when commanders on the base learned details of the pre-dawn shooting spree in which 16 Afghan civilians were killed in their homes. At that point, the 38-year-old Army veteran was taken into custody. He refused to talk further and soon asked for a lawyer, two officials said.

The accounts contradict widely published reports suggesting that Bales had confessed to a crime after the shootings. The account of Bales’ first statement implied he might have asserted a legitimate military purpose for his alleged unauthorized foray to two nearby villages.

A U.S. official said the Army’s Criminal Investigative Command, which is conducting the investigation into the case, is “looking closely at his story that he had killed some people.”

The officials stopped short of calling Bales’ alleged statement a confession, and it could not be learned if he had provided commanders at Combat Outpost Belamby, a small Special Forces base in Panjawi district, with a fuller account of his actions that night.

Asked by reporters last week if Bales had confessed, Defense Secretary Leon E. Panetta also hedged, saying, “I suspect that that was the case.”

In revealing details about Bales’ alleged statements after the shooting, U.S. officials may be attempting to undermine claims by his defense lawyer that his client had little memory of what happened that night.

Defense attorney John Henry Browne, told CBS News that Bales “has no memory of … he has an early memory of that evening and he has a later memory of that, but he doesn’t have memory of the evening in between.”

Browne said he will not mount an insanity defense for Bales, but will argue that his client suffered from “diminished capacity,” like an emotional breakdown.

Bales is being held in solitary confinement in an Army prison at Fort Leavenworth, Kan. The Army is expected to bring formal charges against him later this week.

According to U.S. officials, Bales left the combat outpost at about 3 a.m. on March 11. He allegedly walked to two nearby villages and went house to house shooting families inside. He had been drinking alcohol before the incident, according to an official briefed on the investigation.

The Army has held off bringing charges against Bales, the officials said, because authorities are trying to make the charges as complete as possible to avoid any criticism that they aren’t conducting a thorough investigation.

The officials asked not to be identified discussing an ongoing criminal investigation.

