The officer, who was based in Abingdon, died after being dragged under the wheels of a vehicle.
The nine are all male and aged between 13 and 30 and were arrested in connection with PC Harper’s death on 16 August.
They have today had their bail extended until mid November.
The 28-year-old hero cop, who recently got married, was attending reports of a burglary in Berkshire last month and died from his injuries after being dragged under a car.
Detective Superintendent Ailsa Kent of the Thames Valley Police Major Crime Unit said: “We have made the decision to re-bail these people while we continue our investigation into the death of our colleague.
“Legal proceedings in this case remain active, and I would remind people to remain cautious and refrain from speculation on social media around the investigation.”