In Le Dan's cinematic vision, a tormented former US army lieutenant returns to Vietnam to personally apologize for organizing the wartime massacre at My Lai.
Dan, 82, has taken the real-life apology which William Calley made in the United States last year and gone a step further with his latest production, "Nhung La Thu Tu Son My (Letters from Son My)", which features some survivors of the massacre.
"I think this is the most important film of my life," Dan, one of the country's most prominent directors, said in a telephone interview from southern Vietnam.
He has finished filming and is finalizing production with hopes of a Vietnamese premiere in September.
Calley was the only US soldier convicted over the killings at My Lai and other hamlets in an area Vietnamese call Son My.
It was one of the darkest moments of the Vietnam War and helped turn US public opinion against the conflict.
The exact toll of the massacre on March 16, 1968 was disputed but US estimates suggested up to 504 citizens were killed, a figure accepted by Dan.
Old men, women and children all unarmed were murdered in the slaughter by Calley's platoon, which other US soldiers tried to stop.
"There is not a day that goes by that I do not feel remorse for what happened that day in My Lai," Calley said last August.
"I feel remorse for the Vietnamese who were killed, for their families, for the American soldiers involved and their families. I am very sorry."
Dan, who has made about 45 films and television shows during his four-decade career, said his desire to make the film was sparked not just by Calley's apology but by Vietnamese reaction to it.
Pham Thanh Cong, a survivor of the killings who directs a small museum at My Lai, said last year that he welcomed Calley's apology, although it came too late.
"I want him to come back... and see things here," Cong said.
Calley has not returned to Vietnam but in Dan's film he does, as the character Peter Cage.
"He was obsessed. He woke up in the middle of the night after nightmares about the killings in Son My. He decided to come to Vietnam to apologize himself," Dan says.
Cage sends emails to his wife every day to convey the emotions he feels on the return trip.
"In the film, he is pitiful. But no one can hate him," Dan says. "I found information on him on the Internet, in the media. I think my character in the film is about 70 or 80 percent of the real William Calley."
Many of the hundreds of people in the film are from My Lai.
A few, like the museum director Cong, survived the killings.
"I felt very moved having a role in this film because my family members and my neighbors were the victims of the massacre," says Cong, who saw his mother and brothers killed at My Lai.
On screen, Cong heads a museum, as he does in real life.
"In my role, I call for agreement and forgiveness," he says.
Dan, many of whose other films featured Vietnamese wartime heroes, said he would have liked Calley to be part of his latest production but there was not enough time to arrange that.
"I think I will get in contact with him later," said the director.
Shooting of the 95-minute movie took place between December and late February in My Lai and surrounding Quang Ngai province as well as Ho Chi Minh City, the former Saigon.
Dan said he and his friends are funding the production themselves at a cost of less than VND10 billion (US$516,000).
He said he settled on Frenchman Gerard Saub, 65, to play Cage after he could not find any Americans in Vietnam who fit the part.
Saub, a former Paris photographer who sailed around the world, said he had done very little acting until, by chance, he happened upon the film crew and was asked to join the production.
"It's very difficult, really difficult," to play the character based on Calley, said Saub, who lives near Ho Chi Minh City and has a Vietnamese wife.
In a year in which the Academy Awards were dominated by "The Hurt Locker", a drama about a US Army bomb disposal squad in Iraq, Dan thinks there could be US interest in his film.
"Of course, I expect my film to be shown in the US," he said.
Calley was sentenced to life in prison but spent about three years under house arrest before president Richard Nixon effectively pardoned him.
The two countries normalized diplomatic ties 15 years ago and Vietnam is now a key economic partner of the US.
"Our nation wants to close the past and look forward to the future," says Cong, the massacre survivor.
He wants the film to act as "a bridge to protect peace" but still hopes Calley will return to My Lai, to personally apologize and help the victims, while working to prevent similar tragedies elsewhere in the world.
"I think after the film is finished, I might send Mr Calley a DVD," Cong says. "I want him to watch the film."