Kabul, Afghanistan (CNN) -- U.S. military officials have yet to gain access to the sites where 17 Afghans were killed in Kandahar, an obstacle that could make it more difficult to prosecute the American soldier accused of the multiple homicides.
U.S. personnel have not been able to collect DNA from the sites or access the areas, although DNA collected by Afghan investigators may have been received, an official said.
However, DNA has been found in blood on the clothing of the suspect, Army Staff Sgt. Robert Bales.
Security issues and lack of permission from citizens present barriers to access.
"We do not have access to the crime scene," said the U.S. official, who has knowledge of the investigation but did not want to be identified discussing an ongoing inquiry.
His account gives new insight into what apparently occurred the night of the March 11 attacks on two villages in the Panjwai district, near a remote U.S. outpost.
His comments on the lack of U.S. access to the sites of the killings also tally with what Bales' attorney, John Henry Browne, told CNN's "Erin Burnett OutFront" late Wednesday.
Browne said that it was "not a traditional crime scene," making it tough for prosecutors to make a case.
"There is no crime scene. The military has not even been back to the villages where this allegation stems from. They haven't been back there. So there's no crime scene, there's no DNA, there's no fingerprints, there's no confession," he said.
"You know, the Afghan people traditionally, I understand, and understandably, bury their dead very quickly. So it's going to be a tough case for the prosecutors."
The U.S. official with knowledge of the investigation said Bales, 38, was meant to have been on duty guarding the base that night, and would have had full body armor and weaponry as standard.
He said he did not think alcohol had fueled the crime. "I do not think that drinking played a big role, but there may have been some level of drinking," the official said.
Bales was allegedly first spotted leaving the base around 1 a.m. by an Afghan guard. It is not clear why the guard did not alert Bales' superiors at that time, and the official said Bales was not noticed when he returned to the compound an hour later.
It was then, during about 30 minutes when he was on the base, that he returned to his accommodation and woke at least one roommate, another U.S. Army soldier, the official said.
"The exact conversation is unclear," the official said, but Bales claimed he had been killing Afghan civilians off the base, which his roommate dismissed as nonsense.
A different Afghan guard then saw Bales leave the base a second time. He alerted his command that someone had left the outpost, and the information was passed to the U.S. soldier in charge of the base.
"The whole base was woken up," the official said, for an accountability check -- a rare instance in which a small unit of soldiers on a base have to count their number.
A search party was then formed, but within a few meters of leaving the compound, it ran into Bales, who had been spotted by a surveillance camera returning toward the base.
That was at 3:30 a.m., about 2½ hours after he first left the base, the official said, stressing that fashioning a precise timeline of that night has been challenging.
U.S. soldiers noticed Bales had blood on him, and he dropped to the ground saying nothing, the official said.
Bales has maintained his silence on the killings since, the official said, his apparent last words to U.S. personnel being to his roommate.
In response to suggestions Bales was traumatized in part by a recent injury to a U.S. colleague, the official said that a soldier at the base had lost a leg in a explosion three or four days earlier but that there was no reason to suspect Bales had been present at the scene of that blast.
In addition to the 17 charges of murder "with premeditation," Bales faces six counts of attempted murder and two counts of assault.
He returned to the United States earlier this month and is being held at Fort Leavenworth, Kansas.