Forty years ago, on May 4, 1970 soldiers opened fire on a student anti-war protest on the campus of Kent State University, nestled around the small, sleepy Ohio town of Kent.
The number of dead - four students, two of them simply heading to class - does not compare to the number of American soldiers ultimately killed in Vietnam: some 57,000.
And the death toll cannot begin to compare to the number of Vietnamese civilians who lost their lives: between 700,000 and 2 million, according to estimates.
But those student deaths were momentous.
"May 4th represented the war coming home to America. And in many ways it was. It was soldiers firing at unarmed people," said Jerry M. Lewis, who was just a young professor at the time of the shootings, an eyewitness who is still troubled by what happened, four decades on.
Of the Kent State killings, President Richard Nixon's adviser Richard Haldeman wrote in The Ends of Power that the 67 rifle bullets fired that day would, metaphorically, ricochet right back into the White House.
"Kent State, in May 1970, marked a turning point for Nixon, a beginning of his downhill slide toward Watergate," Haldeman writes.
Four days before the killings, Nixon had announced that the American war in Southeast Asia was spreading from Vietnam to Cambodia - where the Communist Viet Cong had set up operational bases.
That announcement, a stunning reversal from Nixon's election promises of a "secret plan to end the war," sparked the initial protests in Kent, on April 30.
But the demonstrations at Kent State on May 4 were also meant to voice anger at the presence of Ohio National Guard soldiers, who had come to occupy the university campus and impose a curfew.
The troops had been sent in by Ohio's tough-talking law-and-order governor, as he campaigned for election to the US senate: during the first protests there had been some vandalism in the town of Kent, and an arson attack on the campus' military officer training centre.
But Kent State was much more than a turning point in the tragicomic story of Richard Nixon, who was kicked out of office because of a break-in organised to spy on the Democratic National Committee, ensconced at Washington DC's Watergate apartment complex.
|Four students were killed, including Elaine Holstein's son, Jeffrey Miller
The killings, and the public outrage which ensued, helped accelerate the end of the war.
"Here were kids who had been brought up to believe that America was different because we had freedom of speech," says Elaine Holstein, whose son Jeffrey Miller was killed.
She remembers how her son had promised her on the phone that nothing would happen to him that day, and how terribly wrong he was.
"I called Jeff's apartment and it rang and rang for quite a while, and some kid picked up, and I said let me talk to Jeff, and he said 'Jeff is dead'," she told us in her small Queen's apartment, her hands trembling as the emotion came flooding back with the memories.
Holstein would teach herself to pretend that Jeff was "just sleeping" in the photographs that were endlessly reprinted in newspapers and magazines, and even displayed in art shows.
The heart-rending snapshot of 14-year-old runaway Mary Ann Vecchio, screaming in anguish, was taken by student photographer John Filo. It would help mobilise some four million outraged students in the nation's first and only nationwide student strike, just days after the killings.
"That clearly had a powerful impact on congress, they started seriously to end the war in Vietnam, they started to cut off the funding" said Alan Canfora, a survivor of the shootings, and an activist who wants Barack Obama, the US president, to open a new investigation into the events of that day.
Despite hundreds of photographs, hundreds of metres of film, and audio recordings of the events, no-one went to jail.
Nine years of lawsuits ended in a carefully-worded expression of regret by the soldiers and the state of Ohio, and a meager financial settlement.
Still, demonstrators against today's American wars told us that Kent State remains an inspiration.
Talking in front of the White House at an anti-war rally in March, 20-something Ryan Smith said: "Back then they were doing it for Vietnam, today we're doing it for Iraq and Afghanistan. All we can say to them [is] that it lives on - the spirit lives on."
And that is how Elaine Holstein feels.
The mother who needs to pretend her son is sleeping just so that she can bear to look at the famous photograph memorialising his death, still feels Jeff's spirit and still sees the ghost of Kent State, when she sees students anywhere in the world stand up to the state.
She says: "To me, the scene I remember is Tiananmen Square, and seeing those students, and thinking 'how wonderful it is that they will dare to do that'."
Four Dead in Ohio can be seen from Tuesday, May 4, at the following times GMT: Tuesday: 2330; Wednesday: 0530, 1430; Thursday: 0030, 1930; Saturday: 2130.