Ian Huntley replaced little-worn tyres on his car the day after he hid the bodies of Holly Wells and Jessica Chapman near a remote track, the Old Bailey was told yesterday.

The school caretaker then tried to bribe a mechanic to write a false registration number on the invoice. This, the prosecution claims, was a calculated attempt to cover his tracks as he "sanitised" his car.

The trial was told yesterday that the "level of suspicion" against Mr Huntley rose in the days leading to his arrest on 17 August 2003 and that he appeared particularly curious about police attempts to contact any "abductor".

The 10-year-old girls disappeared from Soham, Cambridgeshire, on 4 August 2002. They were found 13 days later near Lakenheath, Suffolk. Mr Huntley, 29, denies murdering them. His former partner Maxine Carr, 26, has pleaded not guilty to two counts of assisting an offender and one of conspiracy to pervert the course of justice.

The court heard yesterday that Mr Huntley took his red Ford Fiesta into a garage on 5 August 2002 and changed tyres that were only a year old. Their tread was in such good condition that a mechanic offered the tyres to another but he was unable to use them and they were destroyed.

Christopher Piggott, a tyre fitter, said he was offered £10 to put a false registration number on the invoice. He passed Mr Huntley's request to his boss and it was complied with.

The car was seized by police 11 days later because, as acting Chief Inspector George Barr put it, "suspicion had increased against Mr Huntley over the duration of the inquiry" and investigators decided to search the home he shared with Ms Carr again.

The jury was told Mr Huntley approached the second- most senior officer on the case after a meeting at Soham Village College where residents were asked to "look at their neighbours" to find the answer.

Mr Huntley questioned Detective Chief Inspector Andy Hebb about a message that had been left on Jessica's mobile phone in an attempt to contact any potential kidnapper.

"Mr Huntley asked me how an abductor would be able to get the message from the police if the battery was dead. Then, after a slight pause, if it had been thrown away," Det Ch Insp Hebb told the court.

After hearing that any perpetrator could call the police directly, Mr Huntley wandered off.

Stephen Coward QC, for Mr Huntley, asked: "It is quite a basic question that anybody might ask?" "It is," replied the officer, "But nobody else did."

The same day, an "animated" Mr Huntley told Catherine Fitzsimons, a Sky News producer, that he thought the police message was a "stupid idea", the court heard. "What if the phone is broken or they don't have it any more," he said.

Speaking to the BBC Look East reporter James Blatch the day before his arrest he asked when police were going to stop searching for the girls. "I think I heard that when the search gets to seven miles it is scaled down," he said.

The trial continues.