"We knew Neil would not receive a fair trial," his father, Clifford Entwistle, told reporters. "We will continue to fight for our innocent son," he added.
Jurors heard that in the days before the bodies were found, Entwistle had surfed the Internet for ways to kill people.
Forensic evidence also linked Entwistle to the murder weapon - a gun owned by Rachel Entwistle's stepfather found with Rachel's DNA on the muzzle and Neil's on the handgrip.
State prosecutors say they believe Entwistle was despondent after sinking deep in debt and took the gun from his father-in-law's collection in a suburb about 50 miles (80 km) away and returned it on the day of the murders.
They said Entwistle may have intended a murder-suicide but instead boarded a flight to London the morning after the killings to return to his family's home in central England.
Prosecutors also argued that he was dissatisfied with his sex life. He performed a Google search for "half-price escorts" and "blonde beauties" along with "how to kill with a knife" days before the murders, a police computer expert testified.
When arrested in Britain, he was carrying a page torn from a London tabloid containing hundreds of ads for women escorts. On the day of the murders, he checked his account with a sex-swingers Web site, an analysis of his laptop showed.
Despite searches of the Entwistle home by family, police and neighbours, the bodies went undiscovered for two days, hidden under a comforter and bed linens in the master bedroom.
Entwistle told police in a telephone call from London he had found his family killed after returning from errands around 11 a.m. Rachel, a Massachusetts native, met Entwistle in England as a college student and married him in Massachusetts.
