A police force has referred itself to the independent watchdog over an alleged double murder after it emerged its officers left the scene shortly before the killings.
The Independent Police Complaints Commission (IPCC) confirmed it was "assessing" if it should investigate the circumstances surrounding the deaths of Pin Chang, 58, and his 50-year-old wife Quoi, at an address in the early hours of Monday July 7.
A 23-year-old man, a relative of the deceased, was arrested on suspicion of murder following the attack at a semi-detached house in Solihull, West Midlands.
He remains in hospital in a critical but stable condition as a result of injuries sustained at the address.
The IPCC said West Midlands Police's referral "was on a mandatory basis due to prior police contact", after it emerged officers had been at the Changs' home along with paramedics, but later left.
The force said officers were first called to the address in Hermitage Road by West Midlands Ambulance Service (WMAS), arriving at 3.56am.
A spokesman said the officers then left at 4.48am, "after liaison with WMAS".
However, the force spokesman added: "Police received a second call at 5.17am from a resident of the address. Officers arrived at 5.33am."
The couple were found stabbed to death at the house.
An IPCC spokesman said: "The IPCC received a referral from West Midlands Police on July 7 relating to the deaths of Pin and Quoi Chang earlier that day.
"The referral was on a mandatory basis due to prior police contact.
"The IPCC received further information from West Midlands Police relating to the incident on July 11 and we are currently assessing the level, if any, of IPCC involvement."
Police have previously said they are not seeking anyone else in connection with the killings.