French and Argentine investigators scoured the charred wreckage of two helicopters in a rugged region of western Argentina on Thursday for clues to what caused an in-flight collision that killed 10 people, including three French sports stars.
The head of Argentina's investigation team promised a meticulous investigation into Monday evening's accident, which killed Olympic swimmer Camille Muffat, yachtswoman Florence Arthaud and boxer Alexis Vastine.
"A very thorough, highly professional investigation is under way," Ana Pamela Suarez, president of the Air Accident Investigation Board, told reporters at the crash site.
Four French experts arrived in La Rioja province on Wednesday. Investigators will be focusing on whether pilot error or a mechanical failure was to blame for the collision during the filming of the reality TV program "Dropped."
Amateur video of the crash shot from the ground showed the two helicopters flying at low altitude when one veered into the path of the other, its rotors appearing to clip the railings or tail of the other helicopter.
Both helicopters then plunged to the ground and burst into flames. Other contestants and production crew standing on the ground a few hundred meters from the helicopters' flight path ran through heavy undergrowth to the burning wreckage but were unable to beat back the flames.
"Those terrible images are there when we wake up," France's former Olympic skater Philippe Candeloro told reporters in Villa Castelli, where the helicopters went down, on Wednesday.
Tributes have poured in from across France and the sporting world for the three stars killed alongside the two military-trained pilots and members of the crew from the ALP-TV production company.
Under a clear sky in the foothills of the Andes mountains, investigators wearing gloves and face masks pored over a destroyed tail rotor, virtually all that remained of one of the helicopters.
Candeloro, a two-time Olympic bronze medal winner, said he had stepped into a production van for some shade moments after the helicopters had taken off, when he heard a large bang and rushed to the crash site.
"It was already too late. We were powerless," he said.