Pc Harper was pulled behind a Seat Toledo for more than a mile after becoming entangled in a tow rope in August 2019, the Old Bailey heard during a retrial.
The driver, Henry Long, 19, was going at a speed of about 42mph along country lanes, swerving from side to side, allegedly in an attempt to dislodge Pc Harper.
Long denied seeing or hearing the officer or being alerted by his passengers Jessie Cole and Albert Bowers, aged 18. However, footage taken from Pc Harper’s patrol car appeared to show Cole turn towards the officer before he jumped into the car after unhooking a stolen quad bike.
Cross-examining Long, Jonathan Laidlaw QC said: “I’m going to suggest you must have been told by Jessie Cole as soon as he got into the car that he had seen Pc Harper and almost been caught by him.
“Something has caused Jessie Cole to turn around.
“Had Pc Harper called out to Cole, ‘Stop, police, we are the police,’ something of that sort, which caused that to happen? Did you hear that?”
Long replied: “No.”
Asked if that was the kind of thing an officer might say, Long replied: “I don’t know, I’m not a police officer.”
Mr Laidlaw said the officer, who weighed 90kg, got “within touching distance of the car” when he became caught in the strap attached to the rear.
He said all three defendants “knew perfectly well” the 28-year-old had almost reached Cole when the car was driven away. Long denied it.
Mr Laidlaw accused him of telling a “really cynical lie” about turning the music up to “drown out the voices” of his passengers as Pc Harper was dragged to his death.
Long said: “I wanted to concentrate on driving and getting away.”
The lawyer went on: “You and the others have to tell this lie, you have to get something loud to cover up the fact that of course the dragging of Pc Harper was causing a lot of noise behind the car and that was why I suggest you invented this lie.
“The truth is you heard all of this but you are not prepared to accept that to the jury, hence the lie about turning the music up.
“So you saw nothing, you heard nothing and you felt nothing?” The defendant replied: “That’s correct.“
The prosecutor suggested: “There were occasions when you deliberately turned the wheel of the vehicle from side to side in an effort to throw Pc Harper because that was obstructing your getaway.
“I suppose your mindset was get away at all costs.”
Long replied: “I did not know he was there.”
Pc Harper had been responding to a report of a stolen quad bike in Stanford Dingley in Berkshire when the incident happened on the night of August 15 last year.
Long, Cole and Bowers, from near Reading, have denied murder but admitted conspiracy to steal the quad bike.
Long has also admitted Pc Harper’s manslaughter, but denied intending to hurt him. The trial continues.