Two U.S. government officials with knowledge of the investigation into Robert Bales, charged yesterday with 17 counts of premeditated murder of Afghan civilians, say the Staff Sergeant returned to his base halfway through the killing spree, the AP reports

U.S. investigators now believe that Bales walked off his base that night and killed several people in one of the villages, then went back to the base. The American officials, who are privy to some details of the investigation, said they do not know why Bales returned, how long he stayed or what he did while there.

He then slipped off the base a second time and killed civilians in the second village before again heading back toward the base. It was while he was returning the second time that a U.S. military search party spotted him. He is reported to have surrendered without a struggle.

That corroborates the testimony of two Afghan guards who spoke with Afghan investigators, one who saw Bales return to the base in Kandahar at 1:30 a.m., the other seeing him leave it at 2:30 a.m. According to U.S. officials, Bales was armed with a 9mm pistol and M-4 rifle the first time he left the base.