The family of a murdered man who had the mental age of a child are "begging" for information about what happened in the moments between when he was last seen and when he was attacked.
Dean Mayley, 24, was on his way to visit his uncle in Greenford, west London, when he was attacked by a group of men at around 5.15pm on Friday .
Mr Mayley suffered from a development disorder which led to him having moderate learning difficulties and the mental age of a nine-year-old. It meant he rarely left home alone, except to visit relatives.
The victim's family said they are desperate for answers about what happened in the time between him getting off the bus at Broadway, at around 4.25pm, and when he was attacked in Ruislip Road 50 minutes later.
His mother Donna Mayley said: "I hope there is somebody, somewhere, who knows something.
"I'm begging you, really - I don't know what to do."
Mrs Mayley said her son was aware of his learning difficulties, which meant he struggled with reading and writing. But it also meant he saw the best in everyone and trusted people easily.
Fighting back tears, Mrs Mayley said: "Dean was v ery vulnerable and easily led, he just wanted to please people all the time.
"He wanted to be an adult, to be like all the other lads.
"It took me a long time to be able give him that independence he wanted, bit by bit.
"He was a creature of habit - he knew how to get the bus and took exactly the same route every time.
"But something went wrong that day and he didn't get off at the usual stop.
"He was very friendly and I'm sure all the shop keepers in Greenford knew who he was. I just hope someone can help us because we will never get closure without knowing what happened."
Mr Mayley was one of four siblings, two of whom have severe learning difficulties. It has made telling them what happened to Mr Mayley extremely difficult, as they are still struggling to come to terms with the death of their father last year.
Mr Mayley's sister, Emma, 25, said: "Dean was very gentle, had a great sense of humour and loved his family.
"But he was vulnerable and didn't know how nasty the world is. Obviously now we know.
"What has happened to him is evil - but we need to know what happened."
Police are currently conducting house-to-house inquiries in Greenford and are also studying CCTV in an effort to trace Mr Mayley's last movements.
The 24-year-old, who was 5ft 6in, was wearing a black North Face hooded jacket, a grey hooded top, blue jeans and white Reebok trainers when he was last seen.
Detective chief inspector Matt Bonner from the Metropolitan Police said: " Dean was a vulnerable young man who had travelled alone to the Greenford Broadway area to visit a relative.
"He had made this journey many times before without incident and there was no reason that this journey should have been any different. Sadly, that was not the case and Dean was later to die following what appears to have been an unprovoked attack.
"We know that he arrived in the Broadway by bus around 16.25hrs and I am keen to piece together his movements between then and 17.15hrs when he was assaulted by three or four males further along Ruislip Road.
"That group of males is responsible for the assault and death of a vulnerable man who would have been in no position to defend himself from such an attack.
"The people who attacked him are simply vicious cowards."
Anyone with information is asked to contact police on 0208 358 0200.