The trial of three people accused of murdering a police officer has been halted due to the coronavirus pandemic.
PC Andrew Harper died after he got caught in a towing strap trailing behind a car on a country road in Berkshire in August 2019.
The Old Bailey jury was discharged on Monday when a third juror began self-isolating, after two other members withdrew from the trial last week.
Henry Long, 18, and two 17-year-old boys deny murder.
Mr Justice Edis said he had taken the decision to discharge the jury with "great regret" and a "heavy heart".
The judge said it was "not sensible to try to carry on" after a third juror began self-isolating when her father tested positive for the virus over the weekend.
Two jurors in the trial, which started on 9 March, were discharged on Thursday because they went into self-isolation.
Mr Justice Edis said although the law permits a trial to continue with nine jurors, the trial into PC Harper's death had not reached the end of the prosecution case and the three defendants had a "right to give and to call evidence".
He said: "The trial cannot finish in the immediate future and the risk that we will lose another juror, or some other person who is essential to its continuation is so high that I have decided that it is no longer in the public interest to take the risk of continuing to convene at court."
The judge said he also considered a case of "this importance" should be "if possible" decided by a jury with more than nine members.
He said he was "deeply sorry" to "those who loved" PC Harper for his decision, and said the case would be listed on 1 June for a review hearing.
The Old Bailey has heard PC Harper and a colleague were responding to a report of a quad bike theft near Sulhamstead, Berkshire, when he became entangled in a tow rope.
The 28-year-old, from Wallingford, Oxfordshire, was dragged for more than a mile and suffered "absolutely catastrophic, unsurvivable injuries".
Mr Long, from Mortimer, Reading, has admitted manslaughter and conspiracy to steal a quad bike.
The two 17-year-olds, who cannot be named due to their age, pleaded guilty to conspiracy to steal a quad bike. The pair also deny manslaughter.