A 52-year-old man has died after being attacked by a dog which had been returned to its owner despite concerns that it was dangerous.
West Yorkshire Police said the man, who has not been named, was out walking with his Yorkshire terrier when he was attacked by another dog in the Sheepbridge area of Huddersfield on Monday.
He died later in hospital.
The incident has been referred to the Independent Police Complaints Commission (IPCC) because the dog involved in the attack was seized by officers earlier this month but returned to its owner after it was determined that it was not a banned breed.
A 29-year-old man, who is the owner of the dog, was arrested in connection with the incident and later released on police bail pending further inquiries.
Detective Chief Inspector Mark Swift said: "Clearly our thoughts go out to the family at this tragic time. They are understandably devastated by what has happened and are being supported by specially trained officers.
"Our investigation is continuing. We believe that the victim was out with his own dog at the time of the attack near to his home address on Riddings Road. His dog, a Yorkshire terrier, was also injured during the incident and received emergency veterinary care."
He said the suspect dog was captured and taken to kennels.
A force spokesman said officers were called to the scene at 9.48am on Monday and found the victim with serious injuries.
He was taken to Huddersfield Royal Infirmary but pronounced dead at 9pm.
The spokesman said that in June this year a dog warden visited the address where the suspect animal was being kept following concerns from members of the public.
A referral was then made to police amid fears the dog may be a dangerous breed, he said.
The spokesman said: "As a result, the same dog was seized by police and, following a screening, it was determined the animal was not a banned breed under the Dangerous Dogs Act. The dog was returned to its owner on August 8."