A bus from Huddersfield to Brighouse was stopped and a man thrown off after a 12-year-old boy told the driver he'd been sexually assaulted by a fellow passenger.
Now police are appealing for the public's help to identify a man they want to speak to about the unsettling report.
The schoolboy was on the back seat of the 549 service on Monday, October 27 alongside the man police wish to speak to.
Partway through the journey, the boy walked down the bus and told the driver that he'd been inappropriately touched by the man on the back seat.
The driver stopped the vehicle at 4.55pm and made the man leave the bus.
But he may not have left the area, as the boy later reported seeing him hanging around Brighouse Bus Station.
Anyone with information about the pictured man's identity or who was witness to the events on the bus is asked to call Calderdale CID on 101.
Information can also be passed to independent charity Crimestoppers on 0800 555 111.
In unrelated investigations, police would like to speak to the people pictured in the image gallery below. The people pictured in the images may be witnesses as well as suspects. If you recognise anyone, contact police on 101 quoting the reference number on the image caption.