Ten people aged between 13 and 30 are being questioned on suspicion of murdering a police officer who was dragged along a road by a vehicle.
PC Andrew Harper, 28, who got married four weeks ago, died on Thursday while responding to reports of a burglary.
He was killed on the A4 Bath Road in the Berkshire village of Sulhamstead.
Thames Valley Police Chief Constable John Campbell said the death of PC Harper had left the entire force “shocked and saddened”.
Mr Campbell said the officer was a “highly regarded, popular member of the team” and his death was a “significant loss” to the force and also to his colleagues and friends.
The 10 boys and men remain in custody at various police stations.
PC Harper was killed at the crossroads of Ufton Lane and Lambdens Hill and Thames Valley Police said it was still trying to establish the exact chain of events.
The force said PC Harper, who became a regular officer in 2011 after joining as a special constable a year earlier, had attended the reported break-in with a fellow officer.
Mr Campbell said: “What we do know is Andrew had been dragged along by a vehicle.”
He said the suspects were detained within about an hour and officers are working “hard and diligently to find out what happened”.
A post-mortem examination is taking place to establish the cause of death.
Mr Campbell said PC Harper was a “highly regarded, popular member of the team”, adding: “Everybody I’ve spoken to about Andrew talked about the incredible personality he was, what a fantastic police officer, and what a great friend and man he was, and he’ll be sorely missed by everybody.
“My thanks go to all those staff and officers who attended this incident, as well as our colleagues at the fire service and also the ambulance service for their professionalism and support at what you can imagine was obviously a distressing scene.”
He said the force’s flags are flying at half mast as a sign of respect “in honour and memory of Andrew”.
The Deputy Police and Crime Commissioner for Thames Valley, Matthew Barber, said he had received messages from members of the public PC Harper had helped.
A domestic violence victim said the officer had given her the confidence to come forward about her abusive partner, Mr Barber said.
“He was clearly a man who, in his short time, touched many lives”, he added.
Relatives of PC Harper paid tributes on social media to the “loveliest person that you will ever meet”.
Maureen Shrimpton wrote: “Just a really horrible day. Our grandson Andrew was killed last night while doing his police work.
“So proud of him. Our love goes to his lovely wife, mum and dad, brother and all of his family and friends.”
The attack on PC Harper is the third time in recent weeks an officer has been seriously hurt in the line of duty.
Metropolitan Police officer Stuart Outten was stabbed in the head on 8 August.
Days later a 42-year-old West Midlands Police officer suffered serious head and pelvic injuries when he was run over with his own vehicle.
Police Federation chairman John Apter said 10 officers had died in the line of duty in the past decade – a figure he called “truly shocking”.
While policing was “dangerous and unpredictable”, it was difficult to ignore the loss of 22,000 officers as a result of budget cuts, he said.
This had left those in the job more vulnerable than they were 10 years ago, he said.
“Society has become a much more violent place and, for some, life is cheap,” he said.
Prime Minister Boris Johnson called PC Harper’s death a “mindless and brutal” crime, adding he was “shocked and appalled” by the attack.
Labour leader Jeremy Corbyn said: “I’m totally shocked at Andrew Harper’s death and my immediate thoughts are condolences to his family and to his colleagues.”
Home Secretary Priti Patel said: “PC Harper died in the line of duty protecting the public and his incredible bravery and extraordinary sacrifice will not be forgotten.”