A terraced house where a Thai man was stabbed to death with a large kitchen knife was being operated as a brothel, murder squad detectives have revealed.

And the victim, who was “brutally” killed in front of his pregnant girlfriend on his birthday, could already have had a wife in the remote Konkhang region of northern Thailand.

Detective Superintendent Dave Pervin, who is leading the investigation, said the incident at 685 Little Horton Lane, Canterbury, Bradford, might have been a planned and targeted robbery that went wrong.

He said: “This was a vicious and brutal attack.”

Floral tributes have been left outside the property.

Shattered glass can still be seen near the back door, where the intruders forced entry to the house.

Four men, who may have been lying in wait before they struck, arrived at the back door at about 1am on Monday.

Two of them went inside, both armed with knives, while the other two remained outside. One of them attacked the victim, stabbing him once in the chest, while the other threatened the victim’s pregnant partner.

After the offenders fled down an alleyway towards Little Horton Lane, the victim staggered outside into the back garden, collapsed and died.

Police, who initially said the man was a 40-year-old, have revised his age to 42. They said he was in the UK on a work permit that allowed him to work as a head chef, but he recently lost his job at a Huddersfield restaurant. He entered the country in early 2008 and had been living at the address for about two months with his girlfriend.

His identity will not be released until family have been informed, but police are working with the Thai Embassy and Consulate to speed the process.

Det Supt Pervin said: “His 40-year-old girlfriend is expecting a baby in November. Quite clearly she is extremely distressed and is being looked after by specialist police officers.”

Det Supt Pervin appealed to brothel owners in Bradford who may have been robbed but had not reported it to get in touch.

He said four Asian men had been seen in and around the area immediately before the attack.

He said: “I want to know who these men are – if you are one of them and are not connected with the murder then contact us so we can eliminate you from our enquiries.”

The four men are described as young Asian men in their late teens or early 20s, wearing dark sports clothing – possibly hoodies. Two of them were wearing beanie-type hats pulled down over their faces. The murder weapon is yet to be found despite extensive searches.

Anyone with information should call Bradford South Police’s helpdesk on 0845 6060606 or call Crimestoppers, anonymously, on 0800 555111. People can also text police on 07786 200806.