The trial heard the 28-year-old died in “truly shocking circumstances” after his ankles were caught in a rope hanging off the car.
Three teenagers have been convicted of killing a police officer during a desperate attempt to evade capture.
PC Andrew Harper was dragged for a mile behind their car, after he tried to stop the group towing away a quad bike, stolen from outside a house in west Berkshire.
The driver, Henry Long, 19, and his passengers Albert Bowers and Jessie Cole, both 18, had denied murder. Long earlier admitted manslaughter and his co-accused were found guilty of the same offence by a jury at the Old Bailey in central London.
They are due to be sentenced next Friday.
PC Harper’s widow, Lissie Harper, said she felt “utterly shocked and appalled” at the verdict, adding that she was “immensely disappointed” they were cleared of murder and she now has her “own life sentence to bear” which will be much worse “than anyone facing a meagre number of years in prison will experience”.
The trial was told that the 28-year-old Thames Valley police officer died in “truly shocking circumstances” after his ankles were caught in a rope hanging from the back of the car.
As the car sped away, PC Harper was knocked off his feet and “swung from side to side” at the end of the rope, which had been used to tow the stolen quad bike.
The court heard how the young officer and his colleague PC Andrew Shaw had been approaching the end of their evening shift with the roads policing unit on 15 August 2019, when a call came over their radio just after 11.15pm.
The teenage defendants had stolen the quad bike from outside a house in the village of Bradfield Southend and were towing it behind their Seat Toledo when they came face-to-face with PC Harper’s patrol car on a country road, around a mile from the A4.
Video from the police car’s dashboard camera was played in court, showing Cole running from the back of the car, where he had been sitting on the quad bike.
At the same time, as the police car edged towards them, Long drove his car on to the verge and past the police vehicle.
A rear-facing camera inside the police car showed a brief view of PC Harper, through the back windscreen, running towards the Seat as it sped off.
The court heard how the force of impact on the officer’s body, as he was dragged along the road, was so severe it ripped off his uniform and personal belongings.
In video evidence shown to the trial, his colleague PC Shaw, who was driving the patrol car, was seen desperately trying to catch up with the suspects’ car.
He picked up the police radio and told the control room: “My colleague PC Harper got out of the vehicle, ran after the vehicle. I’ve now lost him.”
As he drove down the country road, he stopped to pick up PC Harper’s stab vest.
When PC Shaw got back inside the patrol car, a message from another colleague further along the road signalled a shocking discovery.
In the transmission, the officer can be heard shouting: “There’s a body in the road, body in the road. Can we go to the body?”
PC Shaw radioed back saying: “That’s probably PC Harper. I’ve just found his stab vest in the road.”
Andrew Harper suffered multiple injuries. He was declared dead by paramedics at the scene.
Within 10 minutes of the officer’s death, a police helicopter spotted the defendants’ car parked up at a council-run travellers’ site at nearby Burghfield Common, its engine still hot and clearly visible on the helicopter’s thermal image camera.
The three teenagers, who all have links to the travelling community, were among 10 suspects arrested in the days after the tragedy.
Senior crown prosecutor Rebecca Waller said: “It has been a very difficult case for us because when the Crown Prosecution Service and Thames Valley Police joined forces, we had 10 in custody and obviously they had all been arrested from the caravan site, with no one saying anything.
“There was no forensic evidence, or in fact direct evidence to link anyone with the vehicle, so it was analysis of phones particularly that linked Henry Long and Albert Bowers to the evening offence.
“Their phones had been put out of the hands of the police and have never been recovered.”
Lawyers for the three defendants told the court their clients had no idea that PC Harper had been caught in the tow rope at the back of their car.
They all pleaded guilty to stealing the quad bike and admitted that they were trying not to get caught when they sped away from PC Harper’s patrol car.
In his evidence, Long said he felt “disgraceful” over the death of the police officer.
He said: “I accept that I killed him from what I was doing, the way I was driving.
“If I was aware, I would have stopped the vehicle, tried to save him.”
Cross-examining Long, Jonathan Laidlaw QC referred to footage taken from PC Harper’s patrol car, which appeared to show Cole turn towards the officer before jumping into the Seat.
Mr Laidlaw said the officer, who weighed 14st 2lb (90kg), got “within touching distance of the car” and all three defendants “knew perfectly well” that was the case.
Mr Laidlaw also accused Long of telling a “really cynical lie” about turning music up inside the car to “drown out the voices” of his passengers.
But Long insisted that was true, telling the court: “I wanted to concentrate on driving and getting away.”
Acting Detective Superintendent Stuart Blaik, who led the Thames Valley Police investigation, said: “The prosecution’s case has never been that these three set out that night to kill a police officer, that’s never been our point.
“The point that we make is that when the police and these three came together in Admoor Lane, they’ve made a decision and their decision was, a jury has heard, that they would get away from police at all costs and each of them said that.
“And that cost has caused Andrew to lose his life.”
PC Harper was married just four weeks before he lost his life. He was due to go on honeymoon within days.
Superintendent Blaik said the subsequent investigation has been extremely difficult for all involved.
“The fact he was a police officer and one of our own, of course it has taken a toll on all of us.
“But you know I’m very proud of what we’ve done. It’s been an incredibly difficult investigation for a whole host of reasons.
“But ultimately what I set out to do when I met the family very early on was to try my best for their sake and for Andrew’s, to establish what happened that night,” he said.