A teenager has pleaded not guilty to manslaughter over the death of PC Andrew Harper.
The 28-year-old officer was killed on the A4 Bath Road in Sulhamstead, Berkshire, as he attended a reported break-in on 15 August.
The 17-year-old boy, who cannot be named, also denied a charge of conspiracy to steal, via video-link at the Old Bailey.
Thomas King, 21, admitted conspiring to steal a quad bike.
The 17-year-old, Henry Long, 18, from Mortimer in Reading, and another 17-year-old boy, are charged with murder, an alternative of manslaughter and conspiracy to steal a quad bike.
Mr Long and the second boy will appear at a further plea hearing on 7 January.
King, from Basingstoke, was granted bail until his sentencing at the conclusion of the trial of the other defendants, which is scheduled to start on March 9.
PC Harper, from from Wallingford in Oxfordshire, died after being dragged along a road by a van.
A post-mortem examination found the Thames Valley Police officer, who got married four weeks earlier, died of multiple injuries.