Detectives investigating the 2008 murder of a Norwegian student feared to have been killed by a billionaire playboy have made a breakthrough, the Met said.
Martine Vik Magnussen, 23, was found dead among rubble in a basement in Great Portland Street, Westminster, after a night out with friends.
On Wednesday, the Met Police said officers had arrested a woman aged in her 60s on suspicion of assisting an offender.
The Regent’s Business School students had been celebrating the end of their exams at Maddox nightclub, Mayfair.
Ms Magnussen’s body was found two days later.
The prime suspect for her rape and murder is Farouk Abdulhak, who fled to Yemen within hours of her death.
Det Ch Insp Jim Eastwood said: “Martine’s family has never given up their fight for justice and in the 14 years since her death they have campaigned tirelessly to keep her in the public consciousness.
“Farouk Abdulhak should be aware that this matter has not, and will not, go away,” he added.
“I’m appealing to Farouk Abdulhak directly: Come back to the UK. Come back to face justice.”
The Met said Ms Magnussen’s family was being kept informed of developments.
On the night she died, Ms Magnussen left the Maddox nightclub with Mr Abdulhak at around 02:00 GMT, and her body was found two days later in the basement of the building where he lived.
A post-mortem examination gave her cause of death as compression to the neck.
An inquest recorded a verdict of unlawful killing in November 2010.