16-year-old has been arrested on suspicion of murder of Afghan refugee Hazrat Wali in.
The teenager remains in custody at a southstation after his arrest, police said on Thursday.
Mr Wali, 18, was wounded during a fight on a footbridge before he collapsed on a busy playing field close to his college inon Tuesday.
A PE teacher who was nearby administered CPR but the teenager died from his injuries in hospital.
Hazrat, who lived in, was a student at Richmond upon Thames College and came to the UK in search of a better life two years ago.
Detectives have been studying CCTV footage from the area while divers have been searching a canal under the footbridge.
A Metropolitan Police spokesman said on Thursday: “Officers investigating the murder of Hazrat Wali in Twickenham have arrested a 16-year-old boy.
“He remains in custody at a south London police station after being arrested on suspicion of murder.”
Police said Mr Wali’s family continue to be supported by specially trained officers.
A post-mortem examination has been scheduled to take place at Kingston Mortuary on Friday, October 15.
Anyone who has information or footage of the incident is asked to call police on 101 or tweet @MetCC quoting 5697/12OCT.
Information can also be provided to Crimestoppers, anonymously, by calling 0800 555 111.