Two criminal trials have collapsed at the cost of tens of thousands of pounds to the taxpayer after jurors decided to investigate the evidence themselves, sparking concerns about the prejudicial influence of the internet.

A judge at Newcastle Crown Court was forced to discharge a jury in a manslaughter trial yesterday when one of the jurors sent him a Google Earth map of the alleged crime scene and a detailed list of 37 questions about the case.

It emerged that the juror, hearing the case against Dale Patterson, 18, who was accused over the death of the 71-year-old taxi driver Raymond Quigley, had been to where the death had taken place, taken his own photographs and carried out research into his own theories about what might have happened on the night.

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A second trial, this time at the Old Bailey and involving an allegation of child cruelty, was abandoned when it emerged that one of the jurors had gone on to the internet to search for information about the defendant, Jasmin Schmidt, a nanny who had worked for a celebrity.

In both cases the jurors had told their colleagues on the panel about the results of their investigations.

Judge David Paget QC, sitting at the Old Bailey, discharged the jury at the trial of the German-born Schmidt earlier this year.

Judge Paget said he had no alternative but to discharge the jury and order a retrial after one of the jurors had uncovered false information about other charges against the defendant which the juror had then communicated to the jury. His comments can only be reported now because of reporting restrictions.

It was, said the judge, becoming "harder and harder" to try cases without prejudice because of the internet. The judge said that at the start of the trial he gave a standard warning that jurors should not use the internet or make their own inquiries and went on: "The juror who found this report went looking for it in defiance of what I said."

He added: "It is very unfortunate for all those concerned and for the tax-payer. The chief consideration is that this defendant receives a fair trial."

Judge Paget said he would be sending the file on the abandoned trial to the Attorney General, Baroness Scotland QC, who decides if anyone should be prosecuted for contempt.

Schmidt was convicted this month when tried on a third charge, and is now awaiting sentence.

Judge David Hodson, at the Newcastle trial, ordered Mr Patterson be found not guilty because of a lack of evidence, but made it clear that he would have instructed the jury to find the defendant not guilty anyway because the trial had been prejudiced.