Police are investigating whether a mother may have jumped off the Humber Bridge with her son after his body was recovered from the river below.
Alison Davies and her son Ryan were last seen on Tuesday
A post-mortem examination is due to be carried out on Ryan Davies, 12, whose body was found in the River Humber.
The search continues for his mother Alison, 40, after they went missing on 11 April from Marple, near Stockport.
Ryan, who was autistic with a mental age of seven, was described by a relative as "cheerful and outgoing".
Police said Ms Davies "may have left the side of the bridge with her son".
A Humberside Police spokeswoman said: "One of the current lines of inquiry... is that she travelled to Hull from Stockport with the intention of doing herself harm.
"CCTV has been recovered from the Humber Bridge and officers will now be looking at images of what appears to be some sort of incident on the walkway on 12 April."
She said police were keeping an open mind about the "incident".
The Coastguard recovered Ryan's body from the river at Swinefleet Haven, near Goole, East Yorkshire, after being alerted by the skipper of a pleasure boat on Sunday.
Humberside Police said they were desperate to find Ms Davies, who suffered from depression. They said she had friends in the city and used to live there herself.
Det Supt Colin Andrews said: "We do not believe Alison had visited Hull for some time but we need to speak to anyone in the area who may have had contact with her recently.
"We must also establish how Alison and Ryan got to Hull and so I would appeal to bus and taxi drivers in the city to think back to last week - do you recall taking a woman and her son to the Humber Bridge?"
Ms Davies' sister Lindsay Cook paid tribute to her dead nephew.
She said: "Although Ryan had Fragile X Syndrome, he was a cheerful, outgoing, friendly boy who loved football and riding his bike.
"He enjoyed company and was loved by all who knew him and will be deeply missed. God bless you Ryan. We love you and miss you terribly."
Ms Cook added: "We would also like to highlight the ongoing plight of families coping with mental health and learning disabilities issues in order to spare other families from experiencing this pain."