A 25-year-old man has been arrested over the shooting of equal rights activist Sasha Johnson.
The mother-of-two remains in a critical condition in hospital after being shot in the head at a party in a back garden in Peckham.
On Wednesday, the Metropolitan Police said the man has been detained on suspicion of conspiracy to murder.
So far two other men have been charged over the shooting, while another four remain on police bail.
Devonte Brown, 18, of Southwark, south London, and Cameron Deriggs, also 18, of Lewisham, south-east London, are both accused of conspiracy to murder.
Ms Johnson, a member of the Taking The Initiative Party, was in the back garden of a house in Consort Road, Peckham, when she was shot.
Detectives are continuing to appeal for anyone with information to come forward by calling the police on 101 quoting reference 1172/23MAY, or Crimestoppers anonymously on 0800 555 111.