A British man whose American wife and baby daughter were found murdered at their US home at the weekend is "not a suspect" in the case, police said last night.

Neil Entwistle is believed to have flown back to the UK from Boston, Massachusetts, a day or two before the bodies of his wife Rachel and daughter Lillian were discovered under a pile of blankets in a bedroom at their home.

A statement issued by Nottinghamshire police said Mr Entwistle was being treated as a "potential witness" by US authorities and said there were no extradition proceedings in relation to him.

A spokesperson said: "On that basis, the police in England and Wales have no legal powers to take executive action. In the circumstances, it is not our role to comment on speculation regarding his whereabouts."

Reports that four plainclothes state detectives boarded a plane to Britain last night have not been confirmed by the Home Office, but it is understood Mr Entwistle is in the UK and has been in contact with American officers investigating the murders.

District Attorney Martha Coakley said last night they believed he left the US late on Friday or early on Saturday. Several sources in the US confirmed he was on a flight from Boston to London on Friday.

Mr Entwistle met his wife at York University.

Mrs Entwistle and Lillian were found dead on Sunday night in their $2,700 a month rented five-bedroom home in the quiet town of Hopkinton.

Ms Coakley told the Boston Globe that investigators had developed a rough timeline that placed Mr Entwistle in Massachusetts when the shootings happened, but insisted he was still only "a person of interest" in the case.

Yesterday's statement from Nottinghamshire Police, the force local to the home of Mr Entwistle's parents Clifford and Yvonne, confirms US authorities see him primarily as a potential witness to the shootings, rather than as the main suspect.

Ms Coakley said earlier the state medical examiner's office's "best guess" was that 27-year-old Mrs Entwistle and nine-month-old Lillian died some time between 1am on Friday and early on Saturday.

But she added: "It's still kind of a blurry timeline, whether he was still in the country or not when the shooting occurred. It does not let him off the hook."

She said investigators were "looking into" widely circulated allegations that Mr Entwistle may have been involved in Internet scams.

Reports have alleged Mr Entwistle ran a website offering what appeared to be "get-rich-quick pyramid schemes" linked to Internet pornography.