Police have released a photograph of the 16-year-old who was stabbed to death in Pimlico.
Hani Hicham Abou El Kheir was taken to hospital on Sunday evening but died later that night.
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Kurt Cochran and his wife Melissa had been visiting London from the US to celebrate their 25th wedding anniversary and were due to fly home.
Rail union RMT have slammed the move saying the company MTR is set to make "a killing at the British taxpayers' expense".
The meeting was arranged in the wake of Wednesday's terrorist murder of four people in Westminster.