Petit attended every day of Hayes' trial, leaving only during the medical examiner's testimony detailing the physical harm done to the three women, saying it was "too hard to hear." Admitting that he cried a lot during the court proceedings, Petit said that he showed up every day because he is the "only face left" in the family.
"I had almost no feeling at all. I think I had marginalized [Hayes]," Petit said of sitting day after day in the same room as his family's killer. "I hated what he did, hated what he stood for, hated the life that he lived."
"It was like death by a thousand paper cuts," said Petit. "You sit there and they talk about the alleged victims and I always think I'll drive you to the cemetery and show you the alleged victims... You want to jump up and say they have names. They were people. Their names are Jennifer, Michaela and Hayley."
Barely able to remember when his father told him his wife and daughters had not survived the attack, Petit said he does remember throwing up again and again and sobbing.
"He said, 'They're all gone,' but you just deny it," said Petit. "Your brain doesn't want to believe it, so you push it out."
It's been nearly four years since the Petit house has been decorated for Christmas, and Petit said he doesn't know if he'll ever celebrate the holiday again. Since the home invasion, Petit said he has remained alone in a room, unable to "deal with the holidays."
Petit has stopped practicing medicine since the murders because he says it is "too hard to focus for sustained periods," which wouldn't be "fair to the patients."
"[Jennifer] would probably want me to go back to medicine," he said. "Hayley and Michaela would just want me to be happy."
Asked by Winfrey if he's thought about starting a new family one day, Petit said he's considered it.
"I've imagined it," he said. "On good days yes, on bad days no."
As for whether he'll ever feel happiness again, Petit said he's "not convinced," though a lot of people tell him "it will happen."
His hardest moments are when everyday activities remind him of his family, said Petit.
"Being in a park and seeing a father and a daughter shooting hoops, being on a bike path and seeing a family riding, just day to day things that people do makes you think about the last time you did them," he said.
"Something I thought about a lot during my grieving is that if you lost your parents you were called an orphan, and if you lost your wife you're a widow. But if you lost your children, what's the word for that?" he said. "I don't think there is a word and it just struck me that maybe it's such a terrible thing, that your children aren't supposed to die, that there wasn't a real world for it."
Since the murders, Petit has dedicated his life to the Petit Family Foundation and charities in both his daughter's names, contribution to which support scholarships for young women and research for Multiple Sclerosis. Hawke-Petit had battled MS prior to her death.
Petit's sister, Hannah Petit-Chapman, was called by investigators to identify Hayley and Michaela following their murders. Hawke-Petit was burned so badly that she was only able to be identified through her dental records.
"I don't regret having done it. I regret having to do it," said Petit-Chapman. "I regret the fact that this evil came into their home."