Claims have been made on the eve of a British man’s trial for murdering his American wife and baby daughter that he continued to search for sex after the killings.

Papers filed by the prosecution with the court in Boston, Massachusetts, allege that Neil Entwistle visited internet sex sites before the killings and continued hunting for sex after he fled to Britain. Mr Entwistle, 29, is said to have had a page torn out of a British tabloid with “hundreds of ads” for escorts and “sexual services” when he was arrested at Royal Oak Underground station in West London on February 8, 2006.

He was also carrying a handwritten note “indicating he was seeking to make contact with a former girlfriend”, the court papers say.

Mr Entwistle’s three-week trial begins in the Boston suburb of Woburn on Monday.

“Evidence that the defendant was actively seeking an adulterous sexual relationship . . . tends to establish the defendant’s apparent dissatisfaction with his sex life with his wife, and are therefore relevant to the jury’s consideration of the defendant’s motive to commit the crimes,” prosecutors wrote.

Mr Entwistle, who has pleaded not guilty, faces life in prison without parole if he is convicted of the firstdegree murder of his wife, Rachel, and their nine-month daughter, Lillian.

The mother and child were found shot dead in bed at the family’s rented home outside Boston on January 20, 2006, when Mrs Entwistle’s mother raised the alarm. The coroner found that Mrs Entwistle suffered gunshot wounds in the torso and head, and Lillian died from a shot to the abdomen. She also had facial bruising.

Mr Entwistle, an IT specialist, flew to his parents in Worksop, Nottinghamshire, buying a one-way ticket and leaving the couple’s BMW and keys in a car park at the airport in Boston.

Prosecutors allege that Mr Entwistle shot his wife and daughter with a .22-calibre revolver taken from his American father-in-law and which he returned before flying to Britain.

Traces of Mr Entwistle’s DNA have reportedly been found on the gun along with DNA from another unidentified person — likely to be a point of contention for the defence.

The district attorney has theorised that Mr Entwistle, overwhelmed by financial troubles and dissatisfaction with his sex life, planned a murder-suicide but backed out of killing himself.

In the latest court filing, prosecutors say that before the killings he did internet searches using the terms “how to kill with a knife”, “knife in neck”, “knife in neck kill” and “quick suicide methods”. Prosecutors plan to introduce evidence that Mr Entwistle trawled the internet for sexual relationships in the months before the killings.

Records have been submitted by Various Inc, a California company that runs an internet site that calls itself “the world’s largest sex and swingers community”. According to the Boston Herald, Mr Entwistle posted an image showing himself sunbathing naked, and logged back on four days before his wife and daughter were killed.

Prosecutors say that Mr Entwistle sent e-mails through the site telling another woman that he was “in a current relationship, but looking for a bit more fun in the bedroom and a very discreet relationship”. Authorities have also requested records from a Gibraltar-based online gambling site where they believe he lost hundreds of dollars in the month before the killings. Mr Entwistle, who met his wife while studying at the University of York, is believed to have been thousands of dollars in debt.

He allegedly told his parents-in-law that he was a “secret agent” for the British Government. But he had failed to get four high-tech jobs in the Boston area and had a series of internet businesses registered to his name.

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