Search for murdered pair's lodger

The couple recently visited Alnwick Castle

Police hunting the killers of a Chinese couple are trying to trace a lodger who they say rented a room from the pair a week before they died.

Zhen Xing Yang and girlfriend Xi Zhou, both 25, were found dead at the flat they shared in Newcastle on 9 August.

Mr Zhen had been tortured before being stabbed to death. The couple's cat was also drowned.

Northumbria Police said they were trying to find the unidentified male lodger, thought to be a student.

The couple died after a "frenzied" knife attack at a flat in Newcastle's West End.

Detectives said information on a seized computer and three mobile telephones indicated that the pair may have arranged forged professional qualifications.

But Det Supt Steve Wade, who is leading the murder hunt, said: "The level of violence used in the killings is completely disproportionate to the level of minor fraudulent activity discovered on the couple's computer thus far.

A layout of the couple's Newcastle flat Enlarge Image

"We must not lose sight of the fact that they are victims of a senseless killing and their parents and friends are left devastated and unable to comprehend what has happened."

Mr Wade said it had emerged the couple advertised one of their bedrooms for rent by placing an advert on a website aimed at local Chinese people, which displayed two photographs of the flat together with a contact mobile telephone number.

He added: "We now believe that an unidentified male rented a room from the couple on or about 1 August.

"On 3 or 4 August Mr Zhen routinely contacted his mother in China via telephone and informed her that he had taken on a new lodger.

"He informed his mother that the new lodger was a student and that he came from the Jinzhou area of Dalian City.

"We have no further information to identify the lodger and enquiries to trace him have so far failed.

"We urgently need to identify this unknown lodger who could have vital information to assist the murder investigation, and to eliminate him from our inquiries."

Xi Zhou (standing, right) during a night out with friends in Newcastle

New images of the couple during a night out and on a trip to Alnwick Castle in Northumberland have been released, along with a floor plan of the property.

The photos were found on a computer recovered from their flat.

The couple's bodies were found by friends in separate bedrooms at the ground-floor flat.

Mr Wade said: "We have set up a stand-alone e-mail address which is [e-mail].

"This has been set up to allow people to contact Northumbria Police and they can leave messages in their chosen language.

"The e-mail address has been set up in response to an internet chat room on powerapple.com where we have posted an appeal in both English and Chinese."