A 15-year-old boy murdered at one of Britain's busiest railway stations in the rush hour may have been killed in a pre-arranged fight, police have said.
Nineteen teenagers are being questioned over the fatal stabbing at London's Victoria Station on Thursday evening.
Police have named the victim as Sofyen Belamouadden, from west London. Tests showed he died from stab wounds.
Those arrested are aged between 15 and 17 and from south London, a Metropolitan Police spokesman said.
Det Ch Insp John McFarlane said: "I believe this was a pre-planned fight - a number of individuals travelled by various bus routes to Victoria carrying weapons
"However I retain an open mind about the motive at this stage."
Police have recovered "a number of weapons" from the scene including two knives.
The "reckless" attack began on the steps of the station before spilling on to the District and Circle line booking hall, police said.
One commuter said that the night before the stabbing, a "screaming" row broke out between 10 to 15 teenagers at the station.
One station ticket office worker, who did not want to be named, said a colleague was "right there" as the attack happened.
Police described the attack as a random act of violence
"The boys attacking [the victim] couldn't have been any older than him as they were wearing a dark blue school uniform," he said.
Another Tube worker said the attackers were wearing school uniform.
The night before the stabbing, commuter John Angeli, 47, from Haywards Heath, West Sussex, said he saw police "struggling" to keep a "tense" row between a group of teenagers under control.
Sarfraz Ahmed, who manages a shop at the station, said youngsters had been causing trouble at the station in the past few weeks.
"One day last week a gang chased a boy into a shop and attacked him and trashed the place."
On Friday, Det Supt Ashley Croft said: "This was a reckless act of violence that has resulted in a teenager tragically losing his life and our thoughts are with his family at this time."