A detective who collapsed and died in Camden was chasing a phone thief at the time.
Detective Constable Adele Cashman, 30, an officer based at Kentish Town police station, was in pursuit when she collapsed in Belsize Park Gardens late on Monday.
She died in hospital shortly later.
The smartphone was snatched out of the hand of a 59-year-old woman in Haverstock Hill and the "much-loved and wholly dedicated" officer chased after two suspects.
Uniformed officers on duty in the area saw the chase and joined Det Con Cashman and requested more help.
A 17-year-old boy was arrested at the junction of Belsize Grove and a second boy, also 17, was arrested and a phone recovered, Scotland Yard said.
The suspects remain in custody at north and central London police stations.
Commander Tony Eastaugh said: "The thoughts of everyone in the Metropolitan Police Service are very much with Adele's family, friends and colleagues at this extremely difficult time.
"Adele worked on both Camden and Wandsworth boroughs and was held in high regard by all who met her. She will be sorely missed by everyone who had the privilege of working alongside her."
Acting Borough Commander Richard Tucker, from Camden Police, said: "Adele was a much-loved and wholly dedicated officer.
"We at Camden are completely devastated at her sudden passing and our thoughts and prayers are with her family and friends at this tragically sad time."
The officer joined the force in 2006 and was stationed at Wandsworth Borough, where she worked as a police constable.
She transferred to Camden in 2010 as a detective.
A post-mortem examination will take place later on Tuesday.