Police last night launched a manhunt after the discovery of a mother and her three children murdered at their family home.
The victims, a woman in her 30s, and her daughter and two sons, aged five to 11, were found at the house they shared with taxi driver Rahan Arshad.
Police said the bodies may have lain there undiscovered for a month and forensic officers faced a "horrendous" crime scene.
Arshad, aged 36, also disappeared around four weeks ago.
Detective Superintendent Martin Bottomley, leading the murder hunt, said he had not yet established if Arshad is the husband and father of the murder victims, but the dead woman was the mother of the children and all five lived in the same house in Cheadle Hulme, Greater Manchester.
"We are keen to trace the fifth occupant of the house, Mr Arshad," he said.
"We are concerned for his welfare. We are treating it as a murder inquiry, therefore we need to speak to him."
Police made the grim discovery at 5.05pm on Sunday evening at the neat £200,000 four-bedroom end terrace on Turves Road.
Last night all police forces in the UK are on alert to find Arshad, last seen a month ago, and Greater Manchester Police are also liaising with police abroad.
Arshad, who is originally from Pakistan, may be driving a silver BMW 320 sports coupe, registration, SC06 HLZ.
Mr Bottomley said police had been called to the house last Friday but when officers first called there was no "immediate concern" for the safety of the family.
But a neighbour is believed to have alerted police two days later after knocking on the door and getting no reply but noticing a smell coming from the house.
A cause of death had not yet been established and postmortems were yet to take place.
Mr Bottomley added: "The bodies may have been lying there for up to four weeks and you can imagine in the hot weather we have been faced with a devastating scene."