[4] On the morning of the massacre, C Company, commanded by Captain Ernest Medina, was sent into one of the village's hamlets (marked on maps as My Lai 4) expecting to engage the Viet Cong's Local Force 48th Battalion, which was not present.

The efforts of veteran Ronald Ridenhour and journalist Seymour Hersh broke the news of the massacre to the American public in November 1969, prompting global outrage and contributing to domestic opposition to involvement in the war.

[31] He remembered that he was shooting old men and women, ranging in ages from grandmothers to teenagers, many with babies or small children in their arms, since he was convinced at that time that they were all booby-trapped with grenades and poised to attack.

Ronald Haeberle's eyewitness account of the massacre, in one instance, There were some South Vietnamese people, maybe fifteen of them, women and children included, walking on a dirt road maybe 100 yards [90 m] away.

[43] William Thomas Allison, a professor of Military History at Georgia Southern University, wrote, "By midmorning, members of Charlie Company had killed hundreds of civilians and raped or assaulted countless women and young girls.

[44] By the time the killings stopped, Charlie Company had suffered one casualty – a soldier who had intentionally shot himself in the foot to avoid participating in the massacre – and just three enemy weapons were confiscated.

[46] Warrant Officer Hugh Thompson Jr., a helicopter pilot from Company B (Aero-Scouts), 123rd Aviation Battalion, Americal Division, saw dead and wounded civilians as he was flying over the village of Sơn Mỹ, providing close-air support for ground forces.

Upon returning to the LZ Dottie base in his OH-23, Thompson reported to his section leader, Captain Barry Lloyd, that the American infantry were no different from Nazis in their slaughter of innocent civilians: It's mass murder out there.

[65]: 196  Later, he changed his stance, writing in his memoir that it was "the conscious massacre of defenseless babies, children, mothers, and old men in a kind of diabolical slow-motion nightmare that went on for the better part of a day, with a cold-blooded break for lunch".

[66] Owing to the chaotic circumstances of the war and the U.S. Army's decision not to undertake a definitive body count of noncombatants in Vietnam, the number of civilians killed at Mỹ Lai cannot be stated with certainty.

"[68] On 16 March 1968, in the official press briefing known as the "Five O'Clock Follies", a mimeographed release included this passage: "In an action today, Americal Division forces killed 128 enemy near Quang Ngai City.

"[69] Initial investigations of the Mỹ Lai operation were undertaken by Colonel Henderson, under orders from the Americal Division's executive officer, Brigadier General George H. Young.

[72]Colin Powell, then a 31-year-old Army major serving as an assistant chief of staff of operations for the Americal Division, was charged with investigating the letter, which did not specifically refer to Mỹ Lai, as Glen had limited knowledge of the events there.

"[74] Seven months prior to the massacre at Mỹ Lai, on Robert McNamara's orders, the Inspector General of the U.S. Defense Department investigated press coverage of alleged atrocities committed in South Vietnam.

[42] Independently of Glen, Specialist 5 Ronald L. Ridenhour, a former door gunner from the Aviation Section, Headquarters Company, 11th Infantry Brigade, sent a letter in March 1969 to thirty members of Congress imploring them to investigate the circumstances surrounding the "Pinkville" incident.

[78] He became convinced that something "rather dark and bloody did indeed occur" at Mỹ Lai, and was so disturbed by the tales he heard that within three months of being discharged from the Army he penned his concerns to Congress[75] as well as the Chairman of the Joint Chiefs of Staff, and the President.

[76] Under mounting pressure caused by Ridenhour's letter, on 9 September 1969, the Army quietly charged Calley with six specifications of premeditated murder for the deaths of 109 South Vietnamese civilians near the village of Sơn Mỹ, at a hamlet called simply "My Lai".

On November 21, National Security Advisor Henry Kissinger emphasized that the White House needed to develop a "game plan", to establish a "press policy", and maintain a "unified line" in its public response.

The White House established a "My Lai Task Force" whose mission was to "figure out how best to control the problem", to make sure administration officials "all don't go in different directions" when discussing the incident, and to "engage in dirty tricks".

[89] As members of Congress called for an inquiry and news correspondents abroad expressed their horror at the massacre, the General Counsel of the Army Robert Jordan was tasked with speaking to the press.

Noting the significance that the statement was given at all, Bill Downs of ABC News said it amounted to the first public expression of concern by a "high defense official" that American troops "might have committed genocide".

[93]: 28 In 1968, an American journalist, Jonathan Schell, wrote that in the Vietnamese province of Quang Ngai, where the Mỹ Lai massacre occurred, up to 70% of all villages were destroyed by the air strikes and artillery bombardments, including the use of napalm; 40 percent of the population were refugees, and the overall civilian casualties were close to 50,000 a year.

[95] In May 1970, a sergeant who participated in Operation Speedy Express wrote a confidential letter to then Army Chief of Staff Westmoreland describing civilian killings he said were on the scale of the massacre occurring as "a My Lai each month for over a year" during 1968–69.

Two days later, President Richard Nixon made the controversial decision to have Calley released from armed custody at Fort Benning, Georgia, and put under house arrest pending appeal of his sentence.

[65]: 196 Some authors[110] have argued that the light punishments of the low-level personnel present at Mỹ Lai and unwillingness to hold higher officials responsible was part of a pattern in which the body-count strategy and the so-called "Mere Gook Rule" encouraged U.S. soldiers to err on the side of killing suspected Vietnamese enemies even if there was a very good chance that they were civilians.

Quaker service workers in the area gave testimony in May 1972 by Martin Teitel at hearings before the Congressional Subcommittee to Investigate Problems Connected with Refugees and Escapees in South Vietnam.

He wrote a public letter to Calley describing the plight of his and many other families to remind him that time did not ease the pain, and that grief and sorrow over lost lives will forever stay in Mỹ Lai.

[204][205] A large black marble plaque just inside the entrance to the museum lists the names of all 504 civilians killed by the American troops, including "17 pregnant women and 210 children under the age of 13.

"[209] The museum also celebrates American heroes, including Ronald Ridenhour who first exposed the killings, as well as Hugh Thompson and Lawrence Colburn who intervened to save a number of villagers.

"[114] On 16 March 2001, the Mỹ Lai Peace Park was dedicated, a joint venture of the Quảng Ngãi Province Women's Union, the Madison Quakers' charitable organization, and the Vietnamese government.