His parents immediately maintained their son's innocence and said he had not received a fair trial.
"We know that our son Neil is innocent, and we are devastated to learn that the evidence points to Rachel murdering our grandchild and then committing suicide," his mother, Yvonne Entwistle, said outside the Middlesex District Courthouse.
"I knew Rachel was depressed. Our son will now go to jail for loving, honoring and protecting his wife's memory," she said.
Prosecutors allege Entwistle was in debt and dissatisfied with his sex life when he shot his family with his father-in-law's gun in January 2006. He then traveled 50 miles to return the gun to his father-in-law's home and bought a one-way airline ticket home to England. He was extradited less than a month later.
The defense called no witnesses, but Entwistle's attorney claimed during closing arguments that Rachel Entwistle shot her baby and committed suicide. Entwistle claimed he returned the gun because he wanted to preserve his wife's honor.
Prosecutors rejected the suicide claim, saying the bullet that killed Lillian went through the breast of Rachel Entwistle, who then would have had to have raised the gun over her head to kill herself.
Jurors deliberated a day and a half before convicting Neil Entwistle of murder and two weapons charges.
Sentencing was scheduled for Thursday morning. In Massachusetts, the sentence for first-degree murder is automatically life in prison without the possibility of parole.
Rachel Entwistle's family did not immediately comment on the verdict.
Prosecutors said Entwistle had been in a downward spiral since moving to the United States four months before the killings. He had been unable to find a job, had had several Internet businesses fail and had just moved into a $2,700-per- month rented home in Hopkinton.
But a police detective testified about computer records that showed Entwistle trolled the Internet for local escort services and joined an online swingers' site.
During the trial, jurors heard Entwistle discuss the killings in his own voice on three hours of recorded phone conversations he had with a state trooper in the week after the murders. He sobbed as a grisly crime scene video depicting the bodies of his wife and daughter was shown to the jury.
Entwistle told police he returned home from running errands on the morning of Jan. 20, 2006, and found his wife and daughter cuddled together in bed, dead of apparent gunshot wounds.
He stammered after Sgt. Robert Manning asked him repeatedly if he had done something "out of character" the day his wife and daughter were killed.
"No, no, no," he said.
"Of course, no, I couldn't do that. Why would I do that?"
He struggled to explain why he never called police or sought medical help for his wife and daughter before flying back to England the day after the killings.
Entwistle told Manning he was distraught and wanted to be consoled by his parents in Worksop, England. "Looking back on it, I don't know why I did things in the way that I did," he said.
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