Embarrassed officials were at a loss to explain how Jean-Pierre Treiber, 45, a double murder suspect, managed to elude detection in the box he had built himself at a workshop in the high security prison of Auxerre, Burgundy.With its hidden human cargo, the box was loaded with dozens of others onto a lorry for delivery to the Yonne region, southeast of Paris.During the 100-mile journey, he broke free and leapt from the lorry. The driver only realised there was a problem once he had reached his destination, when he spotted a hole in the tarpaulin covering the boxes, some of which were flattened.Police have sealed off roads and a huge area of woodland in the hunt for Treiber using helicopters and sniffer dogs.Treiber has been in prison awaiting trial since 2004, charged with murdering French actor Roland Giraud's daughter Geraldine, and her friend Katia Lherbier.He is due to stand trial early next year in a case that shocked France.Treiber is believed to have sneaked inside a cardboard box at 10.30am on Tuesday while he was left alone in a prisoner's workshop.He had earlier told guards that he had an afternoon meeting with his parole officer – and nobody noticed his absence until later that evening, giving him seven hours to make good his escape.