Police have released CCTV images of a man wanted in connection with the discovery of hydrochloric acid on a train.
Middlesbrough station was evacuated and closed after a passenger reported a burning smell on board a Northern Rail train to Darlington at around 7.16pm on Sunday.
The hazardous liquid was left in a drinks bottle in the middle of the train.
Emergency services, including firefighters and an ambulance, were called to the station as a precaution due to the fumes from the highly corrosive substance.
Detective Inspector Mick Jackson, of British Transport Police, said: "We have been making enquiries, including checking CCTV, to ascertain how and why the bottle came to be on the train, and believe the man pictured may be able to help.
"If you know him, we would like to hear from you."
Police do not believe the discovery was terror-related.
Anyone with information is asked to call 0800 405040 quoting the log reference B4/ NEA of 14/01/2012.