A day after being convicted of the murders of his wife and baby, Neil Entwistle was sentenced Thursday to life in prison without parole.

The sentence is mandatory under Massachusetts state law. Entwistle's parents and lawyers vowed that his conviction for double murder would be appealed.

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The British man was found guilty Wednesday of shooting 27-year-old Rachel Entwistle and 9-month-old Lillian Rose to death in 2006. Jurors took a day-and-a-half to convict him of two first-degree murder charges and two weapons charges.

"These crimes are incomprehensible," said Middlesex County Superior Court Judge Diane Kottmyer. "The sentence for first-degree murder is fixed by law. It is life without the possibility of parole."

Entwistle, 29, did not speak at his sentencing hearing. He smiled slightly as he entered and left the courtroom.

Rachel Entwistle's mother and stepfather urged the court to give their son-in-law a pair of consecutive life sentences, one for their daughter and one for their granddaughter.

"Our dreams ... have been shattered," Rachel's mother Priscilla Matterazzo told the court in a victim impact statement. "I have lost two generations of my family."

The judge said she understood their request, but imposed concurrent life sentences instead. Consecutive life sentences, she explained, would be purely symbolic as there is no chance Entwistle will ever be released from prison unless the governor pardons him.

Prosecutors argued that the young husband and father was despondent over debt and dissatisfied with his sex life when he fatally shot Lillian and Rachel in their Hopkinton, Mass., home and then fled to his native England.

Middlesex District Attorney Gerry Leone commended the jury's verdict, saying Entwistle was held accountable for "reprehensible, shameful and cowardly acts."

Meanwhile, juror Richard Vantour told the Boston Herald that the panel wanted justice for the man's baby girl.

The case was so draining, he said, it was like "having a week's worth of hard labor packed into each day."

An alternate juror, Andrew Tringale, called the defense's argument that Rachel Entwistle killed her baby and then herself "unrealistic" in comments made to The Boston Globe.

The defense did not call any witnesses, but contended that Rachel Entwistle shot Lillian and then committed suicide while the two snuggled in bed.

Tringale questioned why the defense team didn't put witnesses on the stand to back the claim, made while cross-examining the medical examiner and during closing arguments.

Entwistle acknowledged that he didn't contact police after he said he found their bodies. He said he returned the .22-caliber gun used to kill them to his father-in-law's house 50 miles away in an effort to preserve her honor.

After the jury handed down its verdict, Entwistle's parents immediately asserted their son's innocence and said he had not received a fair trial. His lawyers plan to appeal.

"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 Wednesday outside the Middlesex District Courthouse.

Click here to read the charges against Entwistle (pdf).

"I knew Rachel was depressed. Our son will now go to jail for loving, honoring and protecting his wife's memory," she said.

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FOX News' Catherine Donaldson-Evans and The Associated Press contributed to this report.