British Transport Police have released a CCTV image of a man they would like to speak to in connection with the incident.
The three separate incidents took place on September 16, 2016, at 5.40am, January 5, 2017, at 5.45am and most recently on July 4, 2017, at 8.17am, at Sunderland rail station, reports the Birmingham Mail.
On the first two occasions a man entered the station and defecated by the south stairs, police said in a statement.
The three separate incidents took place at Sunderland rail station
On the most recent occasion the man defecated in the south lifts, and after each incident he travelled by metro towards Newcastle.
Officers are keen to speak to the man in the CCTV image in connection with the incident as they believe he could have information that could help with the investigation.
Anyone with any information is asked to call British Transport Police on 0800 40 50 40.
Alternatively, you can text 61016 citing reference 290 of 10/07/2017.