The trial of John William Cooper, the Pembrokeshire farm labourer accused of four murders, was suddenly stopped today.
The judge, Mr Justice John Griffith Williams, discharged the jury.
A new jury is being sworn in and the trial is expected to restart from the beginning later today.
The trial, at Swansea Crown Court, was in its fifth day when Mr Justice Williams said a matter had been brought to his attention which had caused him to discharge a member of the original jury.
That had led to the whole of the jury being discharged.
Cooper, of Spring Gardens, Letterston, near Haverfordwest, Pembrokeshire, denies murdering millionaire farmer Richard Thomas, 58, and his sister Helen, 56, at their home at Scoveston Park on December 22, 1985.
Cooper also denies the murder of Oxfordshire holidaymakers Peter and Gwenda Dixon, aged 51 and 52, in June, 1989.
Cooper also denies raping a 16-year-old girl, indecently assaulting another and trying to rob money from a group of five youngsters, all on March 6, 1996.
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