Sandra May was a British Transport Police policewoman who lived in London, England during the 2010s. In 2018, she was ordered by the BTP to investigate the train after the BTP put out a report of a possible suicide bomber attempting to board a London-bound service; MPS sergeant David Budd noticed her looking around the train, and, having himself witnessed a suspicious South Asian man board the train, he approached May and revealed himself to be a policeman. May said that the suspicious man might be in the bathroom, and she told Budd about the BTP's plan to have the train stop at the derelict Barnet Shed depot, where SCO19 would board the train. Budd had May give him her name and number, and he kept in touch with her as he investigated the threat on the train. He told her to unlock the train doors in the case of an evacuation, and he also told her when he found one of the bombers, Nadia Ali, whom he talked out of blowing herself up. Budd had May tell SCO19 that the female suicide bomber was cooperating, ensuring that the police did not shoot Nadia on sight. When the train was stopped, both Nadia and her husband were arrested, and a terrorist attack was averted.