Final CCTV image of a despairing mother and her autistic son

They look like any mother and son arriving at a railway station at the start of an Easter day out. But just over an hour after CCTV footage captured Alison Davies and her son Ryan, both probably leapt 100ft to their deaths from the Humber Bridge.

Humberside Police released the images yesterday as part of their search for Ms Davies, 40, who remains missing five days after the body of her son was found upstream of the bridge. As they did so, a fuller picture emerged of the personal strain that Ms Davies was under as she struggled to raise a son with Fragile X syndrome, a genetic condition with similar traits to autism which meant he had a mental age of seven.

Ms Davies's troubles appear to have been compounded when a support group for children with disabilities, where she met parents facing similar difficulties, closed three years ago through lack of funding. That deepened her sense of despair according to one friend, Tracey Hinds, who has two disabled children and attended the same group, at a local primary school.

"[The group] was a place where you could go to meet other parents in the same position as yourself and swap advice and get some support," said Ms Hinds. "There was less support for her again [when it shut]. The only time she got to herself was when her mum used to look after Ryan for her and maybe once a week when social services stepped in for an hour. But it wasn't enough. She just didn't get the help she needed. You have to fight for everything when you are looking after children with disabilities because if you don't fight for it, you don't get it."

Although Ms Davies suffered from depression, her decision to take her son away - so that her family "would not have to worry any more" - came at a time when new possibilities had opened up in her life. She had just started a new job, finally passed her driving test and was busying herself with home improvements at her house.

A few days before the disappearance, Ms Hinds had arranged to help her with some tiling and to put up a blind. "She was around at my house the week before she went missing," said Ms Hinds. "She used to take my daughter out shopping with her and she would stay overnight with Alison and Ryan. They used to all play the guitar together."

Despite suffering from Fragile X syndrome, Ryan was a pupil at mainstream Hazel Grove High School and had two passions in life: riding his bike and watching Manchester City.

Another family friend, Debbie Williams, saw Ryan as he cycled past her on the evening before he and his mother disappeared. "I said 'all right Ryan'? and he answered 'yes'," said Ms Williams. "He was a lovely lad with an inquiring mind. In 2004, we took all the children from the estate on a coach trip to Southport. He was chatting with everyone. He was a happy little boy."

Jean Millns, 71, a neighbour of Ms Davies, said she had known both mother and son for 10 years. "Every time Manchester City lost, Ryan came to me and said 'They've lost again, what are we going to do about it?'" She said Ryan's mother would "always take the time to speak" when they saw each other in the street.

Yet beneath the veneer of normality, Ms Davies was struggling. After arriving at Hull railway station, shortly before 2.40pm nine days ago, she and her son made for the bridge where Ms Davies made a 999 call to Humberside Police. Shortly before 4pm, CCTV images captured two people climbing over the railings and falling from the footpath of the bridge into the water. A taxi driver may hold more clues to the intervening hour. Detective Superintendent Colin Andrews said: "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 their lives," .

Post-mortem examinations on Ryan have proved inconclusive but there were no signs of any physical injury before his death.

The National Autistic Society said the case highlighted the pressures facing families coping with children who have such disabilities. "If one good thing comes out of the tragedy it is an awareness of the lack of support for respite care," said a spokeswoman. "Local authorities are reluctant to pay for support."

Four-and-a-half years ago, Helen Rogan, another single mother who was struggling to cope with the needs of her autistic son, threw herself and the 11-year-old boy to their deaths from a railway viaduct near their home in Co Durham. An independent report into the tragedy called for greater help for carers.

Stockport social services said it was inappropriate to discuss the level of respite care granted to Ms Davies. "Ryan attended mainstream school. He received additional support in accordance with his needs," it said.

Margaret Lambton and Harriet: The 'relentless grind' of living with the condition

Margaret and Nigel Lambton from Brampton, Cambridgeshire, have two children, Alex, eight, and Harriet, five, who has severe autism. Nigel is a squadron leader in the RAF and spends a lot of time away from home, leaving his wife as Harriet's full-time carer.

Margaret, 39, says: "It is the relentless grind that can wear me out at times. Even the simplest things take so much time. Getting dressed, even getting her upstairs to get dressed can take a lot of time. School mornings are horrendous. Getting her to eat a bowl of cereal can take 20 minutes."

"We almost never go out, because it is such a major task it just feels easier not to bother. I sometimes feel that it would have been easier if Harriet had a physical disability. I think people are more sympathetic to that. With Harriet you can see people noticing that something is not quite right and maybe think she is just naughty. That can make being out really stressful."

Nigel, 35, says: "I get concerned that Margaret has to cope on her own. We don't get respite care and sometimes when I talk to her on the phone I can hear the strain in her voice."