A 16-year-old boy found fatally stabbed in a stairwell of a block of flats after a party has been named by police.
Peter Hagan was pronounced dead after being discovered on the ground floor of the block in Wandsworth, south-west London, at 1.30am on Sunday.
A Metropolitan police spokesman said: "Although we await formal identification, we are satisfied the victim was Peter Hagan."
A postmortem examination started on Sunday and was due to resume later on Monday.
A murder investigation has been launched and an incident room has opened in Sutton, south London, under Detective Chief Inspector Nick Scola of the homicide and serious crime command.
Nine people have been arrested in connection with the inquiry, Scotland Yard said. Eight have been bailed pending further inquiries and the ninth currently remains in custody.
Police cordoned off a stretch of road outside Albon House, in Neville Gill Close, as forensics teams examined the scene on Sunday.