Looking for Gilles Caron (Histoire d'un Regard) documents the life of French photographer Gilles Caron, who went missing in Cambodia in 1970 at the age of thirty, through some of the startling, often moving 100,000 images which he took in the course of his work.

The Cambodian king, Norodom Sihanouk, had been deposed by Lon Nol on March 18 1970. On April 5th of that year, Caron disappeared after taking a ferry across the Mekong Delta.

His last-known whereabouts were on Route 1, a road between Cambodia and Vietnam, controlled by Pol Pot's Khmer Rouge. Journalists had been going missing and a Japanese journalist who was beer seen again is mentioned. The film, however, offers no clues as to how Caron went out of sight, seemingly forever.

Married to Marianne, and the father of their two daughters - Marjolaine Caron, one of Gilles' daughters, is a key contributor - Gilles had gone on assignment to Cambodia reluctantly. He did not feel comfortable at the Hotel Royale in the capital Phnom Penh, he felt lonely and under pressure. "If I could, I'd take the first flight to Paris," he wrote in a letter to his wife.

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The young father, who had co-founded the Gamma photo agency years before, was feeling parental responsibilities. It seems that he had reported from war zones for long enough. In Jerusalem, he had covered the Six-Day War in 1967, later on he was in the thick of the Vietnam War - his batch of dramatic pictures from battle failed to make the cover of Paris Match because of a flight delay. He covered conflicts in Mexico and in Chad, where he and a number of other photographers were detained.

He worked in Biafra in Nigeria (twice), in Prague and Derry. His photographic record from Prague, in revolt against the Soviet invasion, and from Derry in the throes of the Civil Rights movement appeared in the same edition of Paris Match in 1969. The previous year, he had covered Les Événements, the riots and protest marches that transformed the streets of his native Paris (he was born in Neuilly) in May 1968.

He took 1,200 photos in just three days in Derry and the film retraces his steps through the city in 1969. Director Mariana Otero revisits Caron's vantage points, his locations, the bird's eye view from the roof of a flat complex, streets once full of rubble. One of his photos shows an assembly of ready-to-use Molotov cocktails. Otero meets individuals who had been participants in, or observers of the street protests and stand-offs with the British Army.

She meets the two sisters of Jim, who was imprisoned at the age of 17, and released three years later at the age of 20. He was shot dead by a British army soldier, while travelling on a bus from the cinema. He was about to turn 21, it was a deliberately targeted killing, the sisters say, even if that would be disputed by the authorities. Now middle-aged, the women fight back tears as they view the scrolling of Caron's images from Derry, hoping to recognise among the many black-and white photographs, the Frenchman's image of their brother.

A friend had written to Gilles in July 1968 to tell him that he had proved himself, that it was time to come home. "Your wife and two children need you," the man told the photographer. Perhaps if he had listened then, Gilles Caron might be alive to tell the story. His humane heart and a complex sense of duty must have prevailed until it was too late.

Paddy Kehoe

Available to rent on IFI@Home from 12 midday on Sunday November 22 to 10.00pm on Wednesday November 25