The father of a college student murdered in south-east London has called his son's killer "a coward".
Samuel Guidera, 24, was stabbed in the heart soon after leaving Penge East station last Saturday night.
Appealing for witnesses to the attack, the victim's father, Chris, warned that the "cowards" would "do it again" if they were not caught.
A 39-year-old man from Penge and a man aged 18 from Sydenham have been bailed until April.
Mr Guidera, an aspiring teacher who was a history and politics student at the University of Greenwich, was found collapsed in Bailey Place, near the station.
He had stopped at a corner shop nearby and was attacked as he walked towards a bus stop on Newlands Park, on his way to meeting a friend.
His mother, Sarah, said the family was "just so angry" at the killing.
She said: "His elder brother Dan is just absolutely devastated. He just can't comprehend it. There is just no motive."
Chris Guidera said: "I just think whoever he is or they are, they are just cowards and if they are not caught they will do it again.
"Because [if] they can do it to some innocent person then you would just think that they have got no conscience."
Det Ch Insp Lawrence Smith of the Metropolitan Police said the student "came from a loving family who are devastated as they struggle to come to terms with his death".
The victim travelled on the 2117 GMT train from Bickley to Penge East, crossing the footbridge to Newlands Park.
At the same time as this service arrived at Penge East, the 2125 GMT train from Victoria to Orpington arrived on the opposite platform.
"We particularly want to hear from people who got off the train at the same time as Samuel," Det Ch Insp Smith said, adding that the student had been carrying a distinctive pink carrier bag.
Officers will hand out leaflets to the public at the scene of the murder on Saturday, exactly a week after the attack, as part of their appeal for witnesses.