One of the teenage suspects in the shooting of five-year-old Thusha Kamaleswaran has been stabbed.
The 17-year-old is in a "serious but stable" condition under police guard in hospital, sources confirmed. He was admitted to hospital with stab wounds on Saturday - a day before his arrest on suspicion of the attempted murder of Thusha and 35-year-old Roshan Selvakumar.
Detectives are keeping an "open mind" over the motive for the attack in south London. The stabbing is not thought to be related to that incident.
Thusha's mother Sharmila Kamaleswaran has said the shooting last week left her "feeling empty inside".
Relatives are maintaining vigils at Thusha's hospital bedside while detectives build up a "continuity trail" of the attackers' movements before the incident at the Stockwell Food and Wine store.
Thusha was hit in the chest and Mr Selvakumar suffered a head wound as two youths cowered in the shop after being chased by three others on bicycles through Stockwell.
The arrested youth is understood to be recovering at King's College Hospital, where medical staff are also caring for Thusha.
The stabbed teenager is one of four suspects arrested in connection with the double shooting in Stockwell.
Kazeem Kolawoli, 18, of Black Prince Road, Lambeth and Anthony McCalla, 19, of Oakdale Road, Streatham, have both been charged with two counts of attempted murder. After appearing at Camberwell Green Magistrates' Court they were remanded in custody for a hearing at the Old Bailey on June 10.
The 17-year-old boy who was stabbed remains in custody, while a 14-year-old has been bailed to a later date.