Photographs taken on the set of Leni Riefenstahl's last film could shed new light on the director's involvement with the Nazis.

Although she denied accusations of collaboration until her death in 2003, Riefenstahl was a favourite of Adolf Hitler, and her films Triumph of the Will and Olympia are widely regarded as pinnacles of Nazi propaganda. However, the harshest allegation levelled against her was that she knowingly used a group of Gypsy children from internment camps as extras during the shooting of Tiefland, her last full-length project, and that those children were shipped to concentration camps when their work was complete.

Now, a collection of photos from the set of the film, purportedly taken by Riefenstahl herself and including several pictures of the children, has been offered for auction by an anonymous vendor. Richard Westwood-Brookes, documents expert for the Shropshire-based auctioneers Mullock Madeley, believes the photos could help to establish what really happened to the children. "If they can be recognised and actually identified, then we're taking a huge step towards solving this mystery once and for all," he says. Also included in the lot is a letter from Riefenstahl, in which she denies that any of the children were sent to concentration camps.

The sale was due to go ahead this week, but the auctioneers have delayed it following a plea from the Travellers' community, who are attempting to raise money to buy the pictures themselves. "They consider these photographs are sacred to them and they have no doubt that the children were murdered," Westwood-Brookes says. "I am more than happy to give them the opportunity."

Phein Reachtagan, a spokesman for the travellers, has negotiated a two-week delay on the sale. "As far as we're concerned, they were part of our people," he says. "We were hoping they would be donated to more relevant bodies to be displayed. Not for profit but to show man's inhumanity to man."