Audaciously and on his own initiative, the pilot, Chief Warrant Officer Hugh Thompson Jr., swooped down and landed the copter. “Mr. Thompson was just beside himself,” Mr. Colburn recalled in an interview in 2010 for the PBS program “The American Experience.” “He got on the radio and just said, ‘This isn’t right, these are civilians, there’s people killing civilians down here.’ And that’s when he decided to intervene. He said, ‘We’ve got to do something about this, are you with me?’ And we said, ‘Yes.’ ” Mr. Thompson confronted the officer in command of the rampaging platoon, Lt. William L. Calley, but was rebuffed. He then positioned the helicopter between the troops and the surviving villagers and faced off against another lieutenant. Mr. Thompson ordered Mr. Colburn to fire his M-60 machine gun at any soldiers who tried to inflict further harm. “Y’all cover me!” Mr. Thompson was quoted as saying. “If these bastards open up on me or these people, you open up on them. Promise me!” “You got it boss,” Mr. Colburn replied. “Consider it done.” Mr. Thompson, Mr. Colburn and Glenn Andreotta, the copter’s crew chief, found about 10 villagers cowering in a makeshift bomb shelter and coaxed them out, then had them flown to safety by two Huey gunships. They found an 8-year-old boy clinging to his mother’s corpse in an irrigation ditch and plucked him by the back of his shirt and delivered him to a nun in a nearby hospital. Crucially, they reported what they had witnessed to headquarters, which ordered a cease-fire. By then, as many as 500 villagers had been killed.