A second man has been arrested following the double shooting in Kilburn, north-west London, on Saturday that left one woman dead and another in a critical condition in hospital.
Nursery teacher Sabrina Moss, a mother-of-one from nearby Neasden, died in hospital after spending the night out with friends celebrating her 24th birthday.
The injured woman, who has not yet been named, was believed to be a friend of Moss.
The two women were shot on Kilburn High Road, outside Woody Grill near Gascony Avenue.
Neither woman was believed to be the intended target of the attack, but they were caught up in gunfire after being in the "wrong place as the wrong time", police said.
One suspect had already been arrested on Saturday in relation to the incident.
The second suspect to be arrested is being held at a north London police station, while the first also remains in custody, police said.
Det Ch Insp John Sandlin, from the Metropolitan Police, said: "I am appealing for anyone who witnessed the shooting, or who saw anything suspicion in the Kilburn area early this morning, 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.
"At this early stage, I believe the two women were innocent parties who were caught in the wrong place at the wrong time."
A second shooting incident was reported about an hour after the shooting, in nearby Queen's Park.
Local resident James Cherry posted on Twitter: "Shots were fired in our back garden at around 5am, Queen's Park, back of Bravington Rd. Assuming connected to Kilburn shootings. Terrifying."
Police were initially investigating whether the crimes were linked to the Notting Hill Carnival, which takes place this weekend and passes nearby.
Friends of the murdered woman posted a series of tributes on Twitter, with many voicing concern for her four-year-old son.
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 should call the incident room at Hendon on 020 8358 0300 or Crimestoppers, anonymously, on 0800 555 111.