Police have released an image of a woman they want to speak to over a missing party goer.
They believe the woman may have seen Edward Gillespie, 38, who was last seen during a Christmas party at the Roydon Marina Hotel on December 22.
Police found a pair of glasses belonging to Mr Gillespie, from Luton, near the marina and discovered his car in the car park of the hotel.
Superintendent Luke Collison said: "Ed has now been missing for a month and the more time that has passed without any contact the more concerned we have become for his welfare.
“Despite an intensive search of the marina and the surrounding area, we still have no hard evidence to indicate what has happened to him and in the absence of that, we continue to keep an open mind.
“So far we have spoken to more than 100 people who were at the marina on the night Ed disappeared but to date the woman in this CCTV has not been traced.
“It is believed she would have seen Ed as she walked through the marina in the early hours of Saturday.
“We hope she can provide us with some useful information as we continue our search and we would very much like for her to make contact with us.”