It has emerged the 24-year-old woman who was fatally shot in Kilburn on Saturday was a nursery teacher.
Sabrina Moss, who had a four-year-old son, was on a night out celebrating her birthday when she was killed.
Police have now arrested a second man in connection with her murder.
Another woman, who was also shot, is in a stable condition in hospital.
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The plaque at number 16 Cowley Street in Westminster marks the brown brick Georgian townhouse where Sir John lived for 31 years.
A man reportedly armed with several knives has been arrested in Whitehall on suspicion of planning a terror attack, police have said.
Metropolitan Police officer, Tom Harrison, has been crawling the course since the race began on Sunday morning.