Col. Tom Collins, a Pentagon-based Army spokesman, declined to release the identity of the person with whom Christopher Winfield spoke or provide details of the person's recollection of the conversation.
Winfield, the father of Spc. Adam Winfield, told The Associated Press last month that he received troubling Facebook messages from his son on Feb. 14 that his colleagues had murdered one civilian, planned to kill more and threatened him to keep quiet about it. Christopher Winfield's phone records show he made several calls that day to Joint Base Lewis-McChord, near Seattle, where his son's unit is based.
Winfield, of Cape Coral, Fla., said he had a 12-minute conversation with a sergeant who told him that unless his son was willing to come forward in Afghanistan, he should keep his head down until the deployment ended, when his claims could be investigated.
Winfield also said he left voice-mail messages at a Defense Department hot line and at the base's criminal investigations division. Collins said investigators have uncovered no evidence of the voice-mail messages.
By the time suspects were arrested in May, three months after Winfield's alleged warning, two more civilians had been killed. Five soldiers have been charged in the killings including Spc. Winfield.
Investigative records, charging papers and defendant statements in the case portray some of the most serious allegations to emerge from the Afghan war: a gruesome plot allegedly led by Staff Sgt. Calvin Gibbs to randomly execute civilians while on patrol in Kandahar Province. Some defendants have said they believed Gibbs would kill them if they blew the whistle. Gibbs denies all charges and maintains the killings were "appropriate engagements," according to his lawyer.
Neither Winfield nor his son's attorney, Eric Montalvo, immediately returned messages seeking comment on Friday. They previously said that Spc. Winfield, who allegedly participated in the third killing, was ordered to shoot after Gibbs, the highest ranking soldier charged, tossed a grenade at the unarmed man.
Montalvo said Winfield deliberately shot high so as not to hit the civilian.
But in a videotaped military interrogation, obtained by the AP from a source involved in the case who asked for anonymity, Spc. Winfield did not mention deliberately shooting high.
"I took a man from his family," Winfield told investigators in the video. "I don't know if it was my bullets that killed him or the grenade that killed him, but I was still part of it. It was horrible."
Winfield said he halted his efforts to bring the plot to light because he believed Gibbs would kill him.
"I wish I was brave enough to do the right thing," he said. "I tried to, but I got afraid."
Investigators finally made arrests when a witness in a drug investigation in the unit reported what he considered to be unjustified kills.