Chief constable Cambell was unable to say why Pc Harper was out of his vehicle when he was struck.
Thames Valley Police confirmed they had opened an investigation into the officer's death and that 10 people, all male and aged between 13 and 30, had been arrested on suspicion of murder.
The home secretary, Priti Patel, said: "I'm devastated and appalled by the tragic death of PC Andrew Harper and my thoughts are with his loved ones, colleagues and the community he served with great pride at this immensely hard time".
'Our thoughts also extend to all of Andrew's colleagues within Thames Valley Police.
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The Thames Valley Police road unit officer's death is the most recent in a spate of cops seriously injured or killed in the line of duty, sparking outrage from elected officials Friday.
Twenty-eight-year-old Pc Andrew Harper, who had married his girlfriend just four weeks ago, was "out of his police vehicle" at the time of the incident.
A marquee was constructed on a lawn at the award-winning wedding venue to host Pc Harper's marriage.
A police investigator at the scene of an incident where a police officer was killed, near Sulhamstead, England, Friday.
Prime Minister Boris Johnson has said he is "deeply shocked and appalled" by the death of "brave" Thames Valley police officer Andrew Harper after he was killed as he attended a reported burglary in Berkshire. Two white tents have also been erected.
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Witnesses said officers were seen searching the inside of a grey BMW that was nearby. 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.
Last week, a Metropolitan police officer, Stuart Outten, survived a machete attack after stopping a van in east London and a West Midlands police officer, Gareth Phillips, was run over by a suspected auto thief in Birmingham.
Deputy Chief Constable Jason Hogg said: "As a force we are devastated at the loss of our colleague and will all be supporting each other at this hard time".
Richard Benyon, Conservative MP for Newbury, told the PA news agency it was an "absolute tragedy" and he hoped "those responsible will be brought to justice".
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