WASHINGTON — The American staff sergeant suspected of killing 16 Afghan villagers had been drinking alcohol — a violation of military rules in combat zones — and suffering from the stress related to his fourth combat tour and tensions with his wife about the deployments on the night of the massacre, a senior American official said Thursday.

 

“When it all comes out, it will be a combination of stress, alcohol and domestic issues — he just snapped,” said the official, who has been briefed on the investigation and who spoke on the condition of anonymity because the soldier has not yet been formally charged.

As new details emerged about possible reasons behind the shootings, the American official said the military was preparing to move the sergeant to a prison in the United States as early as Friday, most likely to Fort Leavenworth, Kan., just a day after he was flown to a detention site in Kuwait from Afghanistan.