Neil Entwistle, originally from Worksop, Notts, was jailed in June 2008 after being convicted of shooting his wife Rachel, 27, and their nine-month-old daughter Lillian in Hopkinton, Massachusetts, on January 20 2006.
The former IT worker left the US the day after the killings. He told police he had left because he wanted to be consoled by his parents in the UK.
He said he found his wife and daughter cuddled together in bed, dead of apparent gunshot wounds, after he returned home from running errands.
Entwistle was extradited to the US for trial where he was sentenced to life imprisonment without the possibility of parole at Middlesex County Superior Court in Woburn, Massachusetts, with the judge calling Entwistle's crimes "incomprehensible".
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Armed police have carried out a raid apparently linked to Wednesday's deadly terror attack in Westminster.
Six addresses have been searched as part of police investigations so far and seven arrests have been made.
A large part of Hagley Road in the south west of the city was cordoned off and later reopened.