A 23-year-old man has been arrested on suspicion of murdering 14-year-old Jaden Moodie.
Jaden was stabbed in Leyton, east London, on 8 January after he was knocked off a moped by a Mercedes.
Ayoub Majdouline, 18, of Lily Gardens in Wembley, north-west London, was charged with the boy's murder on 21 January.
The man arrested on Thursday has been taken to an east London police station for questioning, police say.
The Metropolitan Police said it was continuing to appeal for information over the teenager's death.
The trial of Mr Majdouline, who is also charged with possession of a bladed article, is due to start at the Old Bailey on 8 July.