The GPS chip from the car belonging to the father of Swiss twins who disappeared a month ago was found in southern Italy on Saturday.
Police and volunteers have been combing the area around Cerignola, where the father threw himself in front of a train on February 3.
They are still looking for the recorder the man is said to have always carried, in the hope that it will provide information about the fate of the six-year old girls.
Meanwhile the chip has been sent to the Milan branch of the manufacturer to be analysed and will probably be sent on to the headquarters in the United States.
A local police official told the AFP news agency that the chip had been buried beneath some stones. He warned that it was not clear whether it would prove to be a major advance in the inquiry.
The police hope that if they can track the man’s movements exactly, they can narrow down the search for the daughters. However, investigators fear he may have done his best to destroy the evidence by taking the GPS device with him when he killed himself. Fragments have already been found near the track and have yielded very little.
The girls, who lived with their mother in the Lausanne suburb of St Sulpice, have been missing since the end of January, when their father failed to return them to their school after they had spent the weekend with him.
In a letter he wrote to his estranged wife just before his suicide he said he had killed them.
The search has involved police in Switzerland, France and Italy.
Police in Marseille said on Friday they believed the father had been in the area of the French town of Montélimar on the night of January 30, and appealed for witnesses.
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