Police have issued CCTV images of a mother and her son in what they say are "the last few hours of their lives".
CCTV from Hull railway station shows the pair arriving in the city
Humberside Police are investigating whether Alison Davies, 40, from Marple, Stockport, and her son Ryan, 12, died by jumping off the Humber Bridge.
They say other images show two people climbing over the railings and falling about eight seconds apart on 12 April.
Police said Ms Davies, who was suffering from depression, left a suicide note.
Post-mortem examinations on Ryan's body, which was pulled from the Humber on Sunday, proved inconclusive but detectives said there were no signs of physical violence.
Alison and Ryan Davies travelled to East Yorkshire a week ago
Police divers spent Wednesday searching part of the estuary as the hunt for Ms Davies continued.
Det Supt Colin Andrews, who is leading the inquiry, said that until her body was found "we do hold on to the hope that she's still alive".
But he added: "When you piece everything together... one has to be honest and come to the conclusion that it's very likely that the people who fell from the bridge are Ryan and Alison."
He said members of Ms Davies's family had asked if they could view the CCTV footage.
"The images are very poor and will need enhancing", said Mr Andrews.
"They're very, very small, you can't identify them, but what you can see are two people who eventually go over the railings of the Humber Bridge on the eastern footpath and then fall down to the water.
"One person goes first and then the second person about eight seconds later. It's very difficult to say which of the two went first with any certainty."
Referring to the contents of the suicide note, Mr Andrews said: "Clearly Alison was in distress, clearly she felt a burden and clearly she felt that she wanted to relieve her family of that burden.
"And she strongly indicated she intended to travel to the Humber Bridge to harm herself and Ryan."
He stressed that Ryan had not been subjected to any physical violence before his death.
"If the images I've talked about were of Ryan and Alison, then when they were on the Humber Bridge, Ryan was not forcibly dragged anywhere, there was no violence between them."
The new images show the pair at Hull's Paragon railway station at around 1440 BST on Wednesday, 12 April.
Mr Andrews said: "We are trying to piece together the last few hours of Ryan's life and in order to do so need to track down anyone who may have information regarding how he and Alison got to the Humber Bridge.
"On the footage they look like a very normal mother and son combination which makes it all the more sad and upsetting that these images show them in what we believe to be the last few hours of both their lives."