Grieving officers have laid floral tributes at the scene where their colleague was killed at the junction of Ufton Lane and Lambdens Hill.
The 10 suspects - aged between 13 and 30 - were arrested at the Four Houses Corner caravan park, near Burghfield Common, within an hour of the incident, Detective Superintendent Ailsa Kent said on Saturday.
It reads: "We confront danger on a daily basis. We come together as a brotherhood at times like this and hopefully your family can take some comfort from that love and support".
Thames Valley Police Chief Constable John Campbell added: "We are all shocked and saddened by the death of our colleague, Pc Andrew Harper".
"What I can say is that we are working hard and diligently to establish what has happened".
A fundraising page set up by Thames Valley Police Federation to support Pc Harper's widow, Lissie, and his family has raised more than £59,000 so far.
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"I'm Sorry for the loss of your colleague and friend buddy", another person wrote on PC Harper's friend's profile picture, "My thoughts are with you".
They added: "The officer's crewmate was shouting, saying "stay with me, stay with me".
PC Harper was from the Roads Policing Proactive Unit based at Abingdon Police Station.
Thames Valley Police officer PC Andrew Harper and his wife, Lissie, celebrating their wedding four weeks ago at Ardington House in Oxfordshire.
Other relatives have said that the couple had a "dream wedding".
The Police Roll of Honour Trust, which commends officers who have died in the line of duty, has said PC Harper's death will be recorded on the list, adding: "His service and sacrifice will never be forgotten".
Jason Hogg, the force's deputy chief constable, said: "Our deepest thoughts at this time are of course with Andrew's friends and family, who are being supported by specially trained family liaison officers".
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Forensic investigators have erected two white tents at the scene and been collecting items from road and taking photographs.
Officers were seen searching the inside of a grey BMW that was there, according to witnesses.
The incident came after a police constable was run over by a suspected auto thief in Birmingham last week.
A POLICE officer who was killed in West Berkshire died of "multiple injuries", a post-mortem has revealed.
On August 8th, London Metropolitan Police Service constable Stuart Outten was stabbed in the head with a machete during a traffic stop of a motor offences suspect.
Prime Minister Boris Johnson said he was "deeply shocked and appalled by the death of a fearless officer on duty".
"Let's just think for a moment of the horror of it, but also for the need for more police officers to be able to respond to disorder in our society, but also the problem of guns and the problem of violence that is growing", he said. He also vowed to see violent offenders locked up for longer as a result of an "urgent review" of sentencing laws.
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