Neil Entwistle was found guilty Wednesday of two counts of first-degree murder in the 2006 deaths of his wife Rachel and their baby, Lillian Rose, in their rented home in Hopkinton. He fled to his native England afterward.
He claims his wife killed the baby and then committed suicide.
"The defendant has the right to put forward whatever he thinks his best defense is," Joe Flaherty, the spokesperson for Rachel Entwistle's family, told CBS News' The Early Show. "People can make their own judgment, but the only judgment that really counts here are the 12 people that decided this case."
During the brief sentencing hearing, Rachel's mother, Priscilla Matterazzo, called Entwistle's theory of a murder-suicide "low and despicable."
"Suffering does not begin to describe what we have been enduring without our beloved Rachel and Lillian," said Matterazzo, who wore a pink rose on her lapel in memory of her granddaughter. "I have lost two generations of my family."
Matterazzo asked that the life sentences be consecutive, to represent the two generations. But Middlesex District Court Judge Diane Kottmeyer said that would be only symbolic since there is no chance he'll be released, and imposed concurrent life sentences.
Entwistle's family continued to support him.
"There is no way our innocent son Neil is guilty," his father, Clifford Entwistle, said before the sentencing. He refused comment afterward.
"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," Yvonne Entwistle said outside Middlesex Superior Court.
"I knew Rachel was depressed. Our son will now go to jail for loving, honoring and protecting his wife's memory."
District Attorney Gerry Leone denounced Entwistle for blaming his wife for the killings.
"I condemn Neil Entwistle for compounding the unspeakable nature of what he has done by disparaging the memory of his wife and vilifying the entire Matterazzo family by his decisions during the course of this trial," he said.
The couple met at the University of York, England, in 1999, where Rachel, who grew up in Massachusetts, had enrolled for a year of study. They lived in England for several years before returning to the United States so they could raise their daughter in the Boston area, near Rachel's family.
Prosecutors said Entwistle slid into a downward spiral soon after the move. He had been unable to find a job, had failed at several Internet businesses and had just moved into a $2,700-per-month rented home.
People who knew the couple testified that they appeared to have a happy marriage and were thrilled with their daughter.
But a police detective testified that computer records showed Entwistle trolled the Internet for escort services and joined an online swingers' site, where he posted a profile saying he was an Englishman who was looking to meet "American women of all ages" for sex.
What's even more disturbing, reports CBS News correspondent Jeff Glor, is that prosecutors say Entwistle searched the Web using the words: "how to kill with a knife."
Prosecutors argued that Entwistle, debt-ridden and dissatisfied with his sex life, fired his father-in-law's .22-caliber handgun into his daughter's chest and then shot his wife in the head. He flew on a one-way ticket to England a day after the Jan. 20, 2006, killings, they said.
The defense called no witnesses during the trial.
Neil Entwistle's defense attorney Elliot Weinstein defended that decision in an interview with Glor.
"It's absolutely important that the prosecution prove its case beyond a reasonable doubt," Weinstein said. "A defendant, neither Neil Entwistle, nor any defendant, should be required or expected to put forward evidence."
Jurors listened to three hours of recorded phone conversations Entwistle had with a state trooper in the week after the fatal shootings.
On the recording, Entwistle struggles to explain why he never called police or sought medical help for his wife and daughter. He explains that he returned the gun used to kill them to his father-in-law's house 50 miles away in an effort to preserve his wife's honor. He says he flew to England because he needed to be consoled by his parents.
"Looking back on it, I don't know why I did things in the way that I did," he tells the trooper.
Entwistle never mentioned the murder-suicide theory during his statements to police.
Entwistle's attorney, Elliot Weinstein, told the jury that police failed to consider suicide because they immediately focused on his client as a suspect.
"Everything that Neil did after finding Rachel and Lillian in that bedroom, he did because he loved them," Weinstein said.
"We remain confident going forward that we will get a reversal because of the rulings on unlawful search of that home in Hopkinton and that's really what our focus will be going forward," Weinstein told Glor.