A couple were racially abused and spat at on a train after getting into a row with a man over how long he had been in the toilet.
Threats were also made towards their children, police say.
The incident happened at around 6.30pm on June 12 aboard a train between Blackpool and Manchester airport .
British Transport Police said the man got on the train at Manchester Oxford Road and went into the toilet.
Read more of today's top stories
A queue of passengers formed outside, and they started to become frustrated by how long he was in there for.
When he eventually came out, an argument erupted.
The man hurled racist abuse towards another man and woman, and threatened their children.
He then spat in the face of the woman before leaving the train.
BTP launched an investigation into the incident last month, and has since released a CCTV image of a man they want to speak to in connection with the incident.
"Officers believe the man in the images may have information that could help their investigation," a spokesman said.
Anyone who knows him is asked to contact BTP by texting 61016 or by calling 0800 40 50 40 and quoting reference 482 of June 12.
