Driver Henry Long, who dragged police officer Andrew Harper to his death, has been found not guilty at the Old Bailey of murder.
The 19-year-old had previously admitted the manslaughter of the newlywed Pc.
His passengers Jessie Cole and Albert Bowers, both 18, were also cleared of murder but found guilty of manslaughter and face years in jail.
Pc Harper’s widow Lissie said she was “immensely disappointed” with the verdict, adding: “No verdict or sentence 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.”
The defendants heard the jury’s verdicts over video link due to problems with a prison van preventing them from being in court.
The trio hugged and held each other’s hands when they were cleared of murder, but Bowers cried out when he learned he had been convicted of manslaughter, PA Media reported.
After the news sunk in, both Long and Cole became distressed, with Long apparently in tears having to be comforted by his co-defendants.
Bowers, however, seemed elated, and could be seen smiling and patting the other two in an attempt to cheer them up.
Pc Harper, 28, from Thames Valley Police, was killed on August 15 near the village of Sulhamstead in Berkshire.
He died from multiple injuries after being dragged under a van, after becoming entangled in a tow rope attached to their Seat Toledo as he tried to apprehend them for stealing a quad bike in Berkshire.
Long drove off at “breakneck” speed, dragging the Thames Valley Police officer for more than a mile along country lanes before he was dislodged, having suffered horrific injuries.
The teenagers admitted plotting the theft and Long pleaded guilty to manslaughter but each denied knowing that Pc Harper was there.
All three were cleared of murder by an Old Bailey jury that had deliberated for more than 12 hours, but Cole and Bowers were found guilty of manslaughter.
Their defence claimed the incident was a “freak event” that none of them could have planned or foreseen.
But the prosecution said at more than 6ft and weighing 14 stone, the defendants must have been aware Pc Harper was being dragged to his death.
A reconstruction suggested that rather than stopping, Long swerved in the road to try to throw him off.
Jurors also saw dashcam footage that appeared to catch the moment Cole turned towards the officer before diving through the window of the getaway car and making good his escape.
Pc Harper’s tearful widow Lissie was comforted by other family members in court as the verdicts at the Old Bailey were delivered.
Justice Edis adjourned sentence until next Friday.
It can now be reported that Long had previously threatened to “ram” a police officer as he chatted with a police community support officer (PCSO).
In the conversation in July 2018, ruled inadmissible during the trial, Long said: “You can’t touch me now ’cos I’ve passed my driving test and if police try to stop me I will ram them.”
Long had previous convictions for battery, being drunk and disorderly and shoplifting.
Bowers also had youth convictions including for battery, criminal damage, sexual assault, and having an offensive weapon.
Their first trial was abandoned the day the nation went into lockdown in March.
In addition to social distancing for the retrial, Justice Edis had also ordered extra security measures amid fears of potential juror intimidation by supporters of the defendants, it can now be reported.
Following the verdicts, Thames Valley Police Detective Superintendent Stuart Blaik said he was “delighted” to get justice for Pc Harper following a complex and challenging investigation.
He said: “The fact he was a police officer and one of our own – of course, it’s paid a huge toll on all of us.
“But I’m very proud of what we’ve done.”
On the impact on the family, he said: “I don’t think you can ever imagine what Lissie has been through, all the family and all his close friends and colleagues.
“It’s just absolutely devastating for them. This whole process of the court trial, having to relive what’s happened and listen in to the grisly detail of how Andrew came to his death.”
Some 800 mourners turned out for his funeral at Christ Church Cathedral in Oxford on October 14.