Detectives are continuing to question a man on suspicion of attempted murder after a stabbing on a London Overground train.
A male victim was seriously injured as the train pulled into Hackney Central Station at about 18:00 BST on Tuesday.
Police said the man was in a stable condition and recovering in hospital.
The arrested man, aged 55 and from Hackney, is also being held on suspicion of possessing an offensive weapon, police said.