Police are appealing for information following an allegation of a sexual assault on a female train passenger.
The offence is alleged to have taken place on board the 7.10pm Lincoln to Skegness service between Lincoln and Sleaford on Friday, September 19.
A spokesman for British Transport Police say a man allegedly attempted to engage in conversation with a female passenger, before trying to kiss her and then exposing himself.
Officers are appealing to passengers who spoke to the female passenger to come forward.
They would particularly like to trace a red-haired man with a bike who left the train at Ruskington and an elderly couple who spoke to police on the evening.
Contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference MSUB/B12 of 1/10/2014 or Crimestoppers anonymously on 0800 555 111.
A 43-year-old from Skegness has been arrested in connection with the incident. He has been released on police bail pending further enquiries until Tuesday, October 21.