Police officer Andrew Harper was dragged for more than a mile along a road and killed in "truly shocking circumstances", a court has heard.
Prosecutor Brian Altman QC told the Old Bailey on Monday that the alleged murder of the 28-year-old constable was "a completely senseless killing".
Pc Harper died from multiple injuries when he was pulled along behind a car after responding to the reported theft of a quad bike from a home near the village of Sulhamstead in Berkshire.
Henry Long, 18, from Mortimer, Reading, and two 17-year-olds, who cannot be named for legal reasons, all deny murdering the Thames Valley Police officer in August last year.
Mr Altman told jurors: "Late at night, on Thursday August 15 of last year, in Berkshire, 28-year-old Andrew Harper, a serving police constable of Thames Valley Police, was killed in truly shocking circumstances.
"With his ankles caught in a strap that was trailing behind a car being driven at speed along a country lane, he was dragged for over a mile along the road surface, swung from side to side like a pendulum in an effort to dislodge him, losing items of his police uniform along the way, with the rest of his uniform being quite literally ripped and stripped from his body.
"When, at last, he became disentangled, he was left with the most awful injuries, from which he died there on the road, surrounded by colleagues who tried in vain to save him."
Mr Harper, left wearing only his socks and boots, suffered injuries that were unsurvivable, the court heard.
The jury was told: "This was a completely senseless killing of a young police officer in the line of duty."
Long has admitted manslaughter, which the younger boys deny, and all three have pleaded guilty to conspiracy to steal a quad bike.
Several members of Pc Harper's family were in court as the prosecution case opened.
Pc Harper, known as "Harps" to his colleagues, was part of Thames Valley's Roads Policing Unit, and had been due to work a 10am to 7pm shift that day.
He was still on duty with crew mate Pc Andrew Shaw at 11.17pm, and they were driving in an unmarked police BMW fitted with emergency lights.
The pair, who were both wearing uniform, answered the call to the reported theft of the quad bike although it was past the end of their shift.
Mr Altman said: "Despite it being well beyond the end of their shift, because they were close and thought they could help, they responded to the call. It was a decision that was to cost Andrew Harper his life."
Prosecutors claim that the three defendants had planned the theft, visiting the home of owner Peter Wallis earlier that day and taking steps to avoid being caught by police.
Mr Altman said: "It is perfectly clear that all three had thought about and carefully planned this criminal enterprise. There was no point going to all this effort to steal a brand new, valuable quad bike only to be caught.
"They had clearly reckoned with the risk they might be stopped by the police. Not only did they wear gloves and disguise themselves with masks, but also they had disconnected all the rear light clusters to the car – brake, side and indicator lights – so that in any pursuit along dark country lanes they could disappear into the night, without trace, as had been their plan."
The court heard that the officers were driving along a country lane, Lambdens Hill, on their way to the call when they met a Seat Toledo, driven by Long, coming the other way.
One of the 17-year-olds was in the passenger seat, and the other was riding the quad bike which was being towed behind the car, attached to the boot lid hinge with a crane strap that formed a loop.
As the cars met, the teenager on the quad bike dismounted, disconnected the strap from the bike and tried unsuccessfully to get into the passenger door of the Seat, as Long began to drive off.
Pc Shaw turned the BMW's emergency lights on, and the teenager ran to jump through the back passenger window of the Seat.
As Pc Harper tried to stop him, the officer's feet were encircled in the crane strap, and he was dragged along as Long drove off.
The court heard that Long drove at an average speed of 42.5mph, leaving a snaking trail of tyre marks, blood and clothing as he swerved across the country lane.