That is, until the dust settles and his instinct to "keep shooting" starts to recede.
For an event that now serves as a reference point for what came before and after - the Khmer Rouge driving victoriously through Phnom Penh and evacuating people from their homes - that perspective came not days, but years later. And not just for Neveu.
"It was, of course, the beginning of something else," he said in a recent interview.
Neveu, who has just re-released his book The Fall of Phnom Penh, which showcases his photographs from that day, has since travelled the world on assignments for Time and Newsweek.
But his first project, one he gave himself as an overambitious 24-year-old, was to cover the secret war in Cambodia which culminated in the fall of Phnom Penh - a story that remains one of his most sought-after.
"It wasn't symbolic at the time. At the time it was the end of a war," Neveu revealed.
"It was the end of hardship; there was a sense of relief," he added.
"It's like the end of a storm, its nice and quiet, you don't see the next storm coming."
Although it is not clear from the photographs he took on that day, Cambodia was about to enter one of the darkest chapters in its history.
The beginning of the country's tumble into tragedy looked more like a day of jubilation and relief, as smiling teenage soldiers raised their flags and guns in the air.
This perspective was caught by few photographers, as only a handful of Western journalists stayed behind after the regime took hold of the capital.
"I feel confident I can explore smaller elements in great detail," Neveu said of the hundreds of frames recorded in The Fall of Phnom Penh: 17 April 1975, reissued this year through Bangkok-based publisher Asia Horizons Books.
Though some of the original negatives were lost in transit between the Gamma Photo agency in Paris and Gamma-Liaison in New York, they were rediscovered in the 1990s when Getty Images bought Gamma-Liaison.
The return of the lost films allowed Neveu to complete the day's narrative.
"It's part of my contribution to fill the gap. I don't go beyond the image. I don't try to tell a different story to the images," Neveu said.
His photographs are studiously portrayed, showing the contact sheets as well as prints, and few descriptions other than the time of day.
He says this helps him defend his role as "voyeur" - particularly when people are unsure why the photographs don't look "sad enough".
"I can't balance it with pictures of people dying because we just didn't see it at the time," he stated.
Neveu admits the photographs in The Fall of Phnom Penh will be viewed differently by Cambodians and foreigners.
He recalls meeting one Cambodian man who sought refuge in the French Embassy during the fall.
Only 14 years old at the time, the man said he had stayed on because he had thought there would be no problem.
"I like the photos because they bring back visual fragments which show that this actually happened," Neveu said.
"People can talk about it, and there is a distance created from talking about it."
Yet despite the power of his own photographs, Neveu says he is simply filling a void.
"For the Cambodians who view the photos, it does fill a gap their lives.
"They have more intimacy with the pictures; it's somehow ingrained in their brain," he claimed.
"Me? I'm detached."