Detectives are today appealing for witnesses after a man was found outside his home in Keighley with serious head injuries.
Police were called to flats in Spring Row at 6.20pm yesterday and discovered a 64-year-old man.
He was taken to Leeds General Infirmary where his condition is described as critical.
Police are appealing for anyone who saw suspicious behaviour or a group of people potentially causing disorder outside the flats at around 6pm yesterday to come forward.
Two men aged 51 and 46 and a 38-year-old woman, all local, were arrested on suspicion of assault and remain in custody.
Detective Chief Inspector Jon Morgan, of the Homicide and Major Enquiry Team, said: "We are continuing to investigate this incident and are treating the matter as a serious assault.
"It is believed the victim may well have been in his home and has stepped outside to deal with a nuisance when he has been seriously assaulted and left until found by a passer-by who contacted the emergency services.
"Although three people have been arrested, we very much need to speak to anyone who saw anything suspicious or has information.
"Anyone who can help can contact the Homicide and Major Enquiry Team on 101 or Crimestoppers anonymously on 0800 555 111."