Detectives have released CCTV images of a man they want to trace in connection with a incident on board a route 21 bus at London Bridge last month.
The incident happened at about 9.30pm on Friday 14 October on board a route 21 bus at London Bridge Station.
The suspect threatened the driver and repeatedly punched the driver's protective screen after being challenged for not having enough money on his Oyster card.
Nobody was injured during the incident.
The suspect is described as a white man in his early 20s with short dark hair. He was wearing a chequered shirt.
The incident is being investigated by the joint Metropolitan Police and Transport for London Safer Transport Command Workplace Violence Unit
Anyone with information is asked to contact Detective Constable Dan Hippey on 020 3054 5403 or Crimestoppers anonymously on 0800 555 111.