The mother was sexually assaulted and strangled. Her two girls died of smoke inhalation after the youngest was sexually assaulted, they were tied to their beds and doused in gasoline, and the house was set on fire.
Steven Hayes, 47, could be sentenced to death. His attorneys have admitted his involvement and will argue for a life sentence.
Prosecutors said Hayes and another ex-con broke into the family's house in Cheshire in 2007, beat the girls' father with a baseball bat and forced their mother, Jennifer Hawke-Petit, to withdraw money from a bank before she was sexually assaulted and killed. Eleven-year-old Michaela and 17-year-old Hayley were tied to their beds, with pillowcases over their heads, before they were killed by the gas-fueled fire, authorities said.
The crime drew comparisons to "In Cold Blood," Truman Capote's chilling book about the 1959 murders of a Kansas family, and prompted more Cheshire residents to get guns. It also led to tougher laws for repeat offenders and home invasions, and Connecticut Gov. M. Jodi Rell cited the case when she vetoed a bill that would have abolished the death penalty.
The girls' father and the lone survivor, Dr. William Petit, appeared to stifle tears as the verdict was read. His head down, he sucked in his bottom lip.
"There is some relief but my family is still gone," Petit said afterward, his father and other relatives clutching him. "It doesn't bring them back. It doesn't bring back the house that we had."
Hayes showed no emotion as he stood for the verdict, which triggers the trial's second phase, beginning Oct. 18, in which the same jurors will decide if Hayes should be executed.
Petit said he hoped the jurors would use "the same diligence and clarity of thought" as they consider the sentence.
Hayes' defense conceded most of the evidence on the trial's first day, but his attorneys blamed his co-defendant, Joshua Komisarjevsky, for escalating the violence at every critical point, starting with William Petit's beating. Prosecutors rejected that argument, saying the two men were equally responsible for the crime.
Komisarjevsky faces trial next year and also could be sentenced to death.
Hayes' jury heard eight days of gruesome testimony and deliberated for five hours over two days.
He was convicted of 16 counts, including six capital felony charges, three murder counts and two charges of sexually assaulting Hawke-Petit. The capital offenses were for killing two or more people, the killing of a person under 16, murder in the course of a sexual assault and three counts of intentionally causing a death during a kidnapping.
During the penalty phase, which is expected to last up to a month, Hayes' attorneys will try to persuade the jurors to spare him the death penalty. They argued during the trial that prosecutors failed to prove Hayes intended to kill the girls.
Attorneys not involved in the case said Hayes' lawyers will have difficulty showing mitigating factors that would favor prison over execution.
"If there was ever to be a hue and cry for the application of the death penalty, this case is it," said defense attorney Bruce Koffsky.
Another defense lawyer, Hugh Keefe, said: "I've never seen a case where the evidence is so egregious. Not even his mother loved him."
Prosecutors have said the crime was especially cruel and depraved.
Komisarjevsky spotted the mother and her two daughters at a supermarket, followed them to their home, then returned later with Hayes, authorities say.
During the trial, authorities showed text messages between the men hours before the crime in which Hayes told Komisarjevsky that he was "chomping at the bit to get started."
Authorities say the men were caught fleeing the scene.
Hayes, still reeking of gasoline, gave an emotionless confession to police in which he said he was financially desperate when the men hatched a plan to break into a house, tie up the family, rob them and flee. But Hayes said "things got out of control," a detective testified.
Hayes told authorities he sexually assaulted Hawke-Petit after Komisarjevsky, 30, told him he had to - to "square things up" - because Komisarjevsky had sexually assaulted Michaela, a detective testified.
A prison officer, Jeremiah Krob, said he overheard Hayes tell another inmate that he killed Hawke-Petit after Komisarjevsky told him he had to do it.
Hayes said Komisarjevsky sexually assaulted Michaela, took cell phone pictures of her that he tried to e-mail to friends and doused her in gasoline, Krob testified. Krob said Hayes admitted pouring gas on the stairs but told the other inmate he didn't believe he could be charged with arson because he didn't light it.
Jurors apparently agreed: They acquitted Hayes of an arson count.
William Petit told the jury he woke up on his couch the morning of July 23, 2007, in pain and feeling the sensation that blood was running down his face. He saw two people standing nearby.
"If he moves, put two bullets in him," Petit recalled one of the assailants telling the other.
Petit said the men took him to his basement and tied him to a post.
Jurors saw photos of the victims, charred beds, rope, ripped clothing and ransacked rooms. A medical examiner described the painful and panic-stricken smoke inhalation death likely suffered by Michaela. Hayley's injuries suggested she managed to free herself and was burned as she tried to flee. She also died of smoke inhalation.
When asked Tuesday how he would find the strength to attend the penalty phase and then another trial filled with the same horrifying testimony, Petit said: "If your family was destroyed by evil, I think you would all try to do the same thing and be there for your family."