A second man has been arrested over the killing of a 24-year-old woman shot dead as she celebrated her 24th birthday.
Sabrina Moss, from Neasden in northwest London, died in hospital after being involved in a double shooting.
Police said she was caught in the wrong place at the wrong time while out with friends.
Another 24-year-old woman remains in hospital. Her condition has been described as critical but stable.
Detective Chief Inspector John Sandlin of the Metropolitan Police said: "Enquiries continue to establish the full circumstances of this tragic incident.
"At this early stage, I believe the two women were innocent parties who were caught in the wrong place at the wrong time."
The family of Ms Moss visited the scene of the shooting on Sunday with flowers, which officers placed inside a police cordon.
The second man is being held at a north London police station, and the first remains in custody, Scotland Yard said.
Police were called at 4.12am yesterday to reports of shots fired in the street in Kilburn High Road, Kilburn, north-west London, at the junction with Messina Avenue.
Police and the London Ambulance Service found two women suffering gunshot injuries and both were taken to London hospitals.
Ms Moss was later pronounced dead.
Mr Sandlin said: "I am appealing for anyone who witnessed the shooting, or who saw anything suspicious in the Kilburn area, to call police.
"In particular, I need to hear from anyone who saw two males who came into the High Road from Messina Avenue and, after the shooting, made off on foot back along Messina Avenue."
The second suspect to be arrested is being held at a north London police station, while the first also remains in custody, police said.
Tributes to Ms Moss flooded onto social networking site Twitter, with many of her friends reporting that she had a young child.
Adjei Adu wrote: "My heart goes out to her family and the lil one she's left behind, sleep well Sabrina Moss."
Leila Hassan tweeted: "My Thoughts Are With Your Family... A Beautiful Young Woman, Mother and Daughter!"
Another tweet read: "Lost the cousin I was close with when I was a child.. R.I.P Sabrina Moss."
Anyone with information that might assist the investigation was asked to call the incident room at Hendon on 020 8358 0300. To remain anonymous, call Crimestoppers on 0800 555 111.