A teenager has admitted the manslaughter of newlywed police officer Andrew Harper, who was dragged under a van in Berkshire last year.
But Henry Long, 18, denied murder and will face trial alongside two others in April.
PC Harper, 28, died from multiple injuries following the incident on August 15.
The Thames Valley Police officer had been on duty when he was killed near the village of Sulhamstead.
Long, 18, from Mortimer, Reading, was allegedly behind the wheel. He appeared at the Old Bailey for a plea hearing by video link from Belmarsh prison wearing a black and white Puma sweatshirt.
When asked for his plea to a charge of manslaughter, he said: “Pardon, was that manslaughter?” before adding: “I plead guilty, guilty.”
Long denied PC Harper’s murder but admitted conspiracy to steal a quad bike.
A 17-year-old co-defendant, who cannot be identified, entered not guilty pleas to PC Harper’s manslaughter and conspiracy to steal.
The boy appeared in court by video link from Wetherby young offenders institute in a grey sweatshirt and wearing a crucifix around his neck.
Previously, another 17-year-old boy has entered not guilty pleas to manslaughter and conspiracy to steal.
A fourth defendant, Thomas King, 21, from Basingstoke, had admitted conspiracy to steal a quad bike.
The three teenagers are due to face a six-week trial at the Old Bailey from March 9.