A man was arrested on suspicion of murdering a police officer, who crashed as he was driving them to a local police station, a chief constable said today.
Pc Joe Carroll, 46, died from injuries he received in the crash on the A69 near Corbridge, Northumberland, at around 2.30am.
The suspect had been arrested for an unrelated matter and was travelling with an inspector and Pc Carroll from Hexham to Newcastle when the vehicle crashed, said Northumbria police Chief Constable Mike Craik.
Mr Craik said in a statement: "It was with great sadness that I learnt of the death of Pc Joe Carroll today while carrying out his duties and I offer my deepest sympathies to his family, friends and colleagues.
"Joe had served for over 24 years and had been a local community officer in Bellingham for the last 13 years.
"He was a much loved and valued member of the community that he served in Bellingham and will be greatly missed by his colleagues who will remember him for his sense of community, his professional motivation and his genuine values.
"He was the kind of local police officer that any community and colleague would wish to have and he will be greatly missed.
"At the moment all I can say is that a man who was already under arrest for an unrelated matter has been further arrested on suspicion of the murder of Pc Joe Carroll and a full homicide investigation is now taking place.
"Because of that I am unable to provide any further details on the incident other than to say that Joe and another officer were involved in a road traffic collision in a marked police vehicle.
"No other vehicles were involved.
"Joe was engaged in the transfer of his prisoner to a police station within the Northumbria Police area."
Neither the inspector nor the prisoner was badly injured, though both were treated in hospital.
The Independent Police Complaints Commission has been informed, as a matter of course, a Northumbria Police spokeswoman said.
The A69, the main route between Tyneside and Carlisle, has been closed in both directions while inquiries take place.
A spokeswoman for the Police Federation, which represents frontline officers, said the organisation did not wish to comment on Pc Carroll's death at this stage.