Steven Spielberg's secret material for the new 'Indiana Jones' movie has been stolen.The director is furious after discovering "confidential" computers and photographs for 'Indiana Jones and the Kingdom of the Crystal Skull' were taken from his Los Angeles offices.Spielberg's spokesman Martin Levy said: "We want to warn the media that anything that is offered is stolen property. They are confidential and proprietary materials. We know it is out there."The movie mogul reported the robbery on September 24 after noticing the items were missing from his headquarters at Hollywood studio Universal Pictures, near the set of the latest 'Indiana Jones' instalment.A man has since been arrested and charged for the robbery, but many of the stolen goods are yet to be recovered and the Los Angeles County Sheriff's Department believe he did not operate alone.Police posed as potential buyers after learning a man had been attempting to sell the valuables to a number of entertainment websites.Sheriff's spokesman Steve Whitmore said: "He is on what is known as parole hold. We believe there's more people involved and don't want to release the name until this plays out."'Indiana Jones and the Kingdom of the Crystal Skull' sees Harrison Ford return as globe-trotting adventurer Indy along with a star cast including 'Transformers' star Shia LaBeouf, Australian actress Cate Blanchett, and British stars Ray Winstone, Jim Broadbent and John Hurt.Last week, the movie was thrown into chaos after a film extra leaked details of the safely guarded plot.The film is the fourth in the 'Indiana Jones' franchise and is due to hit screens worldwide in May 2008.