Steven Hayes apologized just before New Haven Superior Court Judge Jon Blue pronounced the sentence that had been recommended last month by a jury that convicted him.
"I am deeply sorry for what I have done and the pain I have caused," Hayes said. "My actions have hurt so many people, affected so many lives, caused so much pain. I am tormented and have nightmares about what happened in that house."
Hayes sexually assaulted and strangled Hawke-Petit. Authorities say he and co-defendant Joshua Komisarjevsky tied the girls to their beds, poured gasoline on or around them and set fire to their home in Cheshire. Komisarjevsky goes on trial next year.
"This is a terrible sentence, but is, in truth, a sentence you wrote for yourself in flames," the judge told Hayes.
Before the sentence was pronounced, Dr. William Petit, who was severely beaten but survived the attack on his family, told the court he had seriously considered suicide after the deaths of his wife, whom he called his best friend, and their two young daughters. Petit fought back tears as he talked about his family.
"I miss my entire family, my home, everything we had together. They were three special people," he said.
The killings, which drew comparisons to the 1959 slayings portrayed in Truman Capote's book "In Cold Blood," were so unsettling that they became a key issue in the death penalty debate in Connecticut's governor's race and led to tougher state laws for repeat offenders and home invasions. Gov. M. Jodi Rell cited the case when she vetoed a bill that would have abolished the death penalty.
Hayes will join nine other men on Connecticut's death row. The state has only executed one man since 1960, so the 47-year-old Hayes will likely spend years, if not decades, in prison.
Defense attorney Thomas Ullmann has said Hayes, who had attempted suicide while incarcerated, had wanted a death sentence.
Hayes' attorneys had tried to persuade jurors to spare him the death penalty by portraying him as a clumsy, drug-addicted thief who never committed violence until the home invasion in Cheshire, a wealthy New Haven suburb. They called Komisarjevsky the mastermind and said he escalated the violence.
But prosecutors said both men were equally responsible and that the crime cried out for the death penalty, saying the family was tormented for seven hours before being killed.
Authorities said Hayes and Komisarjevsky broke into the house, beat William Petit with a baseball bat and forced his wife to withdraw money from a bank while the rest of her family remained under hostage at home. Hayes then sexually assaulted and strangled her, authorities said.
Komisarjevsky is charged with sexually assaulting their 11-year-old daughter, Michaela. He has blamed Hayes for escalating the crime.
The girls died of smoke inhalation.
During the trial, jurors heard eight days of gruesome testimony and saw photos of the victims, charred beds, rope, ripped clothing and ransacked rooms.
Several of the jurors attended Thursday's sentencing, though they were not required to be there.
Paula Calzetta said she went because she wanted to follow through to the very end. Joel Zemke, the jury foreman for the guilt phase, says he feels he's part of "something bigger."
Some jurors say they took advantage of counseling that was offered to them.
Ian Cassell, the foreman for the penalty phase, said the counseling helped him deal with the aftereffects.