Detectives hunting the killer of a family of four found stabbed to death in their home have named a businessman as a suspect they want to speak to.
Anxiang Du, 52, is said to have had business dealings with Jifeng Ding, who was murdered with his wife Helen Chui and their two daughters Xing and Alice in Wootton, Northampton.
Detectives have also appealed for information about a missing car that could hold vital clues about their deaths.
Police said the hired silver Vauxhall Corsa was last seen outside the family's home last Friday.
Their bodies were discovered by police on Sunday night after concerned neighbours raised the alarm.
Mr Du, who lived in Coventry and worked at a Chinese herbal medicine shop in Birmingham, was named as a suspect at a press conference at the headquarters of Northamptonshire Police.
Detective Superintendent Glynn Timmins, who is leading the quadruple murder hunt, told the media briefing that the suspect was a business associate of Helen Chui.
Warning the public not to approach Mr Du, Mr Timmins said: "He is a suspect in this murder inquiry - we want to seek the public's assistance in finding Mr Du so that we can question him about this incident.
"The public should ring 999 if they see the car or indeed Mr Du - my advice would be that neither Mr Du nor the car should be approached."
It also emerged that Mr Du left a suicide note at his workplace before he was last seen on the day of the royal wedding, and was then reported missing to West Midlands Police.
Officers have recovered Facebook postings made by Alice, 12, and Xing, 18, on the day of the royal wedding and believe that all the victims were alive on Friday morning.
Post-mortem examinations showed that Mr Ding, a lecturer at Manchester Metropolitan University, his wife, who was a part-time teacher, and their two daughters all died from stab wounds.
Mr Du, who is originally from China, is described as being of slim build and routinely wears a baseball cap.
Mr Timmins, who said he did not believe the killings were gang-related, confirmed that Mr Du was thought to have left his home in Coventry at 10.30am on Friday.
The businessman then travelled to the shop where he worked in Birmingham city centre, but left his workplace later that morning.
"The link we are pursuing is the association through business interests between Mr Du and Helen Chui," Mr Timmins told reporters.
The detective added that the business interests were complex, but were thought to be legitimate.
Mr Timmins declined to disclose exact details of the note left by Mr Du for family members, but confirmed that it "appeared to be saying goodbye".
Conceding that he may already be dead, Mr Timmins added: "We have no idea where Mr Du may be at the moment - that's why we are seeking the assistance of the public.
"My assumption is that he is still alive."
It also emerged that police, who are continuing fingertip searches around the Ding family's home in Pioneer Close, have yet to recover any murder weapon.
Meanwhile, inquiries are continuing to trace relatives of Mr Ding and his wife, who both originated from the Hang Zhou area of China.
Mr Timmins said he did not believe there was a general threat to the public and that Mr Ding, an expert in polymers who was known as Jeff, and the female family members were "tragically targeted" because of their business interests.
But the officer stressed that the public should exercise caution if they spot Mr Du or the Vauxhall Corsa, which has the registration plate BG60 PMO.
In a statement, Manchester Metropolitan University said it was shocked and saddened by the news of the deaths.
The statement read: "As a senior lecturer, Jeff was a popular and dedicated member of staff who joined the university in 2004.
"Dr Ding taught chemistry and was also active in schools liaison and led a successful chemistry admissions team.
"He was also a respected hall warden, where he provided pastoral support and guidance to many students."
The statement continued: "Jeff will be very sadly missed by all his colleagues in the division of chemistry and environmental sciences, all our staff, students and his friends at Manchester Metropolitan University and by the wider academic and research communities.
"The university is offering counselling and support to Jeff's students and colleagues at this time."
Detectives are attempting to establish how the family's killer travelled to their home on an upmarket estate built on the site of a former army base.
When he was last seen, Mr Du was wearing a white baseball cap, a brown waist-length coat, grey trousers, a blue woollen top and black leather shoes.
"He's likely to be frightened," Mr Timmins said of the suspect. "He's likely to be quite desperate and certainly when and if he sees this in the media, he's certainly going to be very anxious and nervous.
"Therefore, the prudent thing to do would be to assume that Mr Du should not be approached."
Northampton High School, where Xing was a pupil, said its staff and students were devastated at news of her death.
In a statement, the school said: "While there has been no formal identification of the bodies found at Pioneer Close, from the police assumption we understand that one of the victims was Xing Ding, who was a student in the sixth form here at Northampton High School.
"We are all devastated at the news; Xing was a wonderful girl, greatly talented in all areas and very popular with girls and staff alike.
"She will be greatly missed and (is) a huge loss to the school community. Our thoughts are with her friends at this sad time."
The statement continued: "Naturally our main concern now is to help all our girls at this difficult time and we have put in place arrangements to support them. Northampton High School is a strong community and we will all work together to make sure our girls are given the help they need as they return to school."