Two teenagers accused of murdering a police officer have admitted conspiracy to steal a quad bike.
The pair, who are both aged 17 and cannot be named for legal reasons, pleaded guilty at the Old Bailey to plotting to steal the bike.
They and a third man, Henry Long, 18, are also accused of murdering PC Andrew Harper, which they deny.
PC Harper died from multiple injuries after being dragged along a road by a vehicle near Sulhamstead, Berkshire.
The 28-year-old Thames Valley roads policing constable, from Wallingford, in Oxfordshire, had been responding to reports of a break-in on August 15 last year.
Long, of Mortimer, Reading, has previously admitted manslaughter and conspiracy to steal a quad bike. The two 17-year-olds deny manslaughter.
Mr Justice Edis warned potential jurors that the case would be "distressing" and urged them to take a "fair-minded and clear-sighted" view of the evidence.
He said there was "no doubt" that PC Harper died "because he tried to help in the pursuit of these defendants who were in the course of trying to escape after stealing a quad bike".
The judge said: "Henry Long accepts that he drove in a way which was dangerous and which caused death. He denies though that he intended to cause any harm to PC Harper.
"For murder, a person must cause death unlawfully and when doing so must intend to kill or at least to do really serious bodily harm."
The case is due to be opened by prosecutor Brian Altman QC on Tuesday, and continue for up to six weeks.