A Metropolitan Police officer has been arrested over the disappearance of Sarah Everard in south London in a “serious and significant development”.
Ms Everard, 33, was last seen in Clapham at about 21:30 GMT on 3 March.
The man was arrested in Kent on Tuesday. Police said he had been off-duty when she went missing but added that the fact he was a serving officer was “shocking and deeply disturbing”.
A woman was also held on suspicion of assisting an offender.
Police said Ms Everard’s family was being kept updated.
In a statement, the Met Police said the man and the woman had both been taken into custody at a London police station.
Assistant Commissioner Nick Ephgrave said: “The arrest this evening is a serious and significant development.
“We will continue to work with all speed on this investigation but the fact that the arrested man is a serving Metropolitan Police officer is both shocking and deeply disturbing.”
During a later statement, he added the officer “was not on duty at the time” when Ms Everard went missing and would only confirm he had been arrested “in connection” with her disappearance.
He also would not say if the officer was known to the 33-year-old.
When asked by reporters if police believed she was still alive, Mr Ephgrave replied: “We are searching as hard as we can to find Sarah, so we really hope that is the case,” he said.
“As a father myself of four young women I can only imagine the anguish that Sarah’s family are feeling at this very very difficult time.”
The arrest comes after officers searching for Ms Everard put up a cordon outside a block of flats near to where she was last seen on Poynders Road and sniffer dogs have been used to search the nearby Oaklands Estate and gardens.
Officers were also seen searching drains along the street where Ms Everard was last seen.
The Met said officers had visited 750 homes in the area as part of the investigation and the force had received more than 120 phone calls from the public.
Friends and relatives have issued appeals on social media to help find the marketing manager, who vanished on her walk home to Brixton after leaving a friend’s flat in Leathwaite Road in Clapham Junction at about 21:00 GMT.
Her family has said it is out of character for her to disappear.
Ms Everard, who is originally from York and attended Durham University, was last seen wearing a green rain jacket, navy blue trousers with a white diamond pattern, and turquoise and orange trainers. She is thought to have been wearing green earphones and a white beanie hat.
She is believed to have walked through Clapham Common towards her home – a journey that should have taken her about 50 minutes.