Detectives investigating the "sickening" murder of a man with learning difficulties who was stabbed in the heart by hooded attackers have released a CCTV clip of some of his last movements.
Dean Mayley, 24, was fatally knifed as he walked along Ruislip Road, Greenford, west London, at around 5.20pm last Friday.
Scotland Yard has released footage of him getting off an E9 bus just under an hour earlier in Ruislip Road East, and walking towards The Broadway.
Detective Chief Inspector Matt Bonner said: "I hope this footage might help people to recall the events that led to Dean's tragic death.
"This was a vulnerable man who would have shown an unusual degree of trust in those who he came across and it is utterly sickening that he should have been set upon in this way.
"Those responsible are clearly dangerous and callous and it is critical that we track them down as soon as possible so that they can be held responsible for their appalling actions.
"These people are not worthy of protection and I would urge anyone with information to call police as soon as possible."
The group of three or four attackers were all black men who wore hooded tops.
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.
Mr Bonner said the attack seems to have been unprovoked and called his killers "vicious cowards".
Yesterday Mr Mayley's mother Donna said: ''I hope there is somebody, somewhere, who knows something.
"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 shopkeepers in Greenford knew who he was. I just hope someone can help us because we will never get closure without knowing what happened.''
Anyone with information can call police on 020 8358 0200 or Crimestoppers anonymously on 0800 555 111.