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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One professor warns of a 'potentially disastrous capacity crunch'.
A number of families were on board the service from London Euston to Stoke. One family left the train early to escape the abuse.
She's called Amy, and was visiting a hospital.