Three teenagers have been convicted of the manslaughter of PC Andrew Harper, who died after being dragged along a road by a car.
PC Harper suffered catastrophic fatal injuries when his ankles got caught in a strap trailing behind a vehicle driven by Henry Long in August 2019.
Long, 19, had earlier admitted manslaughter but was cleared of murder.
Albert Bowers and Jessie Cole, both 18, were cleared of murder but found guilty at the Old Bailey of manslaughter.
Speaking outside court, PC Harper's widow Lissie said she would feel "heart-wrenching pain" for the rest of her life over the "brutal and senseless killing".
She said she was "immensely disappointed" by the manslaughter verdicts and had been left "utterly shocked and appalled".
Following the convictions, it can now be revealed jurors in the trial had to be given special protection after police received intelligence associates of the killers had planned to intimidate them.
PC Harper was dragged for more than a mile along country lanes in Berkshire after he and a colleague responded to reports of a quad bike theft on 15 August, jurors heard.
Their shift had officially ended four hours before.
The 28-year-old newlywed became "lassoed" to the back of a Seat Toledo after he "unwittingly" stepped with both feet into the loop of a tow rope as he tried to apprehend one of the defendants.
Prosecutors said the Abingdon-based roads policing officer was "swung from side to side like a pendulum" after Long sped off to escape the scene.
The court heard the Seat travelled for more than a mile towards the A4 before PC Harper became detached and died in the road.
Jonathan Laidlaw QC previously told jurors the defendants had been prepared to use force "if met with resistance".
The trio had a large axe, three crowbars and a hammer and were "plainly determined to steal the quad bike" from a home near Stanford Dingley, Mr Laidlaw said.
It was clear they were "intending, if met with resistance, that serious harm would be caused to commit the offence of theft or to secure their escape", the court heard.
During the trial, the prosecution said it had sought murder charges after alleging the defendants were aware the officer was being dragged behind the car.
Defence lawyers claimed the incident was a "freak event" that no-one could have planned or foreseen.
PC Harper, from Wallingford, Oxfordshire, had been married for just four weeks to his childhood sweetheart before his death.
Within weeks, he and his wife had been due to have their honeymoon in the Maldives.
Speaking after the verdicts, Mrs Harper said: "No sentence or verdict will ever bring my incredible, selfless and heroic husband back.
"The results from this trial I had hoped would bring justice - but in reality make no difference to the heart-wrenching pain I will continue to feel for the rest of my life.
"Andrew was taken from us on that horrendous night last year, his life was stolen and the lives of his family and friends altered forever."
She added that she now faced her "own life sentence" which would be "much more painful" than those who would be imprisoned for causing her husband's death.
At the Old Bailey
By Michael Race, BBC News
Proceedings against PC Andrew Harper's three teenage killers have been plagued by disruption.
As the country went into lockdown over Covid-19, the first trial collapsed two-thirds of the way through the prosecution's case.
Security at that trial in March had been stepped up after police said they had uncovered a possible plot by "associates of the defendants to intimidate the jury".
When a new jury was sworn in three months later for the retrial, there were strict social distancing guidelines in place.
Towards the end of the second trial, on 17 July, a juror was seen by a prison officer mouthing "goodbye boys" to three defendants as she left the courtroom.
Mr Justice Edis discharged her, saying her "surprising conduct" could be seen as a "display of partiality towards these defendants".
The 11 remaining jurors, who were not present when the actions of their fellow juror were discussed, were told they would continue to try the defendants and the juror's removal had nothing to do with the facts of the case.
It took them 12 hours and 22 minutes of deliberations to reach their verdicts.
Long, from College Piece, Mortimer, Reading, pleaded guilty to manslaughter but denied murder along with Bowers and Cole.
Cole, of Paices Hill near Reading, Bowers, of Moat Close, Bramley, and Long all admitted conspiracy to steal a quad bike.
The defendants are due to be sentenced next Friday.
Jaswant Kaur Narwal, Chief Crown Prosecutor for Thames and Chiltern, said: "This is a truly heart-breaking case in which a young police officer with everything to look forward to tragically lost his life in the line of duty.
"He was killed trying to stop suspects who were prepared to go to any lengths to get away with their crime."
She said the case was "quite simply" that the defendants were "intent on causing serious harm to anyone who got in their way".
"It has been an emotional trial, and evidentially challenging, but I am pleased the jury has found all three culpable for PC Harper's death," she added.
"My thoughts remain with all of his family and his colleagues at Thames Valley Police."
Thames Valley Police Chief Constable John Campbell paid tribute to PC Harper's family, saying: "They have been through something that no family should ever have to face, but they have shown the most incredible dignity and bravery every step of the way and they have had to do all of this in the public eye."