A Londoner is thought to have jumped off the Humber Bridge, after travelling to Hull from the capital by train.
Police are trying to find two cyclists who passed the man on the bridge last Wednesday.
A bag was found the same afternoon, containing belongings thought to be those of the missing 22-year-old.
CCTV footage caught a man in dark clothing, who appears to be carrying a rucksack similar to the one found, walking along the southbound east footway between 4.05pm and 4.10pm.
Later footage shows the figure appear to go over the railings on the bridge and disappear into the water around 5.05pm.
It also shows two cyclists riding towards Hull from Barton. Officers think they may have seen the man before he went over the side. Police want to speak to anyone else who was walking on the bridge and who may have seen the man, described as Asian and with short, dark hair.
The man’s body has not been recovered.
A police spokeswoman said: “The witnesses we hope will come forward so they can provide us with a description and help us confirm whether or not it is the person we suspect it is.”
Call police on 101 referring to log 549 of November 11.