A female police officer died while chasing down cellphone thieves, according to police reports.
Adele Cashman, 30, had given chase to the young thieves moments after they stole a woman's phone.
Colleagues rushed to help her, but she died 90 minutes later in a hospital.
Investigators are awaiting the results of a post-mortem examination to discover what caused the death of the police detective in Belsize Park, north London, United Kingdom.
A colleague said that Miss Cashman, who participated in triathlons, was exhausted by the pressure and long hours of fighting street crime.
However, she had secured her transfer of joining the Met's Trident team, a specialized unit to combat gang related crime.
Dozens of colleagues traveled to the site to lay flowers, while flags flew at half mast at police stations.
Scotland Yard Chief Bernard Hogan-Howe said: "Adele was there to be brave. It is a terrible loss to all who knew her.”
The tragedy occurred after a woman aged 59, had her cell phone stolen in Camden around 9:30 p.m. on
Ms. Cashman pursued her attackers and was accompanied by a uniformed patrol agent, who requested backup on their radios.
The detective, who was working undercover, joined the chase with a male colleague.
They saw one of the suspects in Belsize Park Gardens, a street where houses cost up to £6 million.
Moments later Ms. Cashman fell down, while in pursuit.
Police and residents went to help her and she was taken by ambulance to the Royal Free Hospital, where she died.