"He knew what he was going to do to our family and he went ahead and did it," said Roby, who worked as a consultant on the TV miniseries, "Blind Faith." (Part 2 airs tonight at 9 on Channel 3.) "For that, I hate him . . . I'll never lose sight of what he did.
"But on the other hand, if right before they're going to give him the lethal injection he admits he did it, then I'd probably talk to him again.
"Right now, he's lying. He's just a liar. And I have no room in my life for liars. That's negative energy."
Roby Marshall and his two brothers, now aged 23 and 19, have been living with unfathomable pain since their father had their mother executed so he could collect $1.5 million in insurance, pay his debts and marry his mistress.
You can get some idea of their ordeal from the miniseries. But you just can't put the depth of the suffering into words or images, said Roby in a phone interview from Los Angeles, where he now lives.
Maria Marshall, a woman as devoted to her sons as they to her, was shot in the back as she and her husband returned to their Toms River home from Atlantic City.
Rob Marshall tried to make the boys believe his lie that he was accosted by highway robbers. The insurance man's manipulations succeeded with his youngest, John, who still thinks him innocent.
"He doesn't even talk about it," said Roby of his little brother. "He just goes in a different direction."
But Roby and middle son Chris overcame their faith in their father and faced the damning evidence that landed him on Death Row. Chris was the first to conclude that his father was guilty. Roby backed his dad until the trial was almost over, when Marshall called his son from prison and asked him to lie in court about his whereabouts on the day of the killing.
Roby confronted his father later in prison. And when Rob Marshall looked away, his son said, and skirted the question of whether he really was a killer, Roby knew. It was their last conversation.
Roby said he still gets occasional letters from his dad, "But they're all the same."
Typically, he said, his father writes about how he was unfairly convicted and encloses a few pages of trial transcript with highlighted passages.
"I don't even read them," said Roby. "I know he did it."
And so he poured out his pain to author Joe McGinniss, who spun it into a bestseller. And then he went to work for NBC on the miniseries.
So why did he want to help spread the story of his intensely personal suffering across the land?
Roby answers matter-of-factly, either from not searching himself deeply or
from weariness at having been asked so many times.
His grandfather - his slain mother's father - asked him to make sure McGinniss told the full story. McGinniss was going to write the book anyway, Roby said his grandfather told him, and the family's destruction should be part of it.
"I promised him," Roby said. "He died four days later."
He sees the miniseries as part of the promise. And part of helping him cope with what he has endured.
He said he had executive decision-making power, shaping dialogue and advising actors on how the real characters behaved.
Some scenes were too painful to watch. One was when his father came home
from the slaying scene and woke him with the news of his mom's murder.
"I couldn't handle it," he said.
He turned away when the actors were staging the actual shooting, but when somebody asked "How much blood?" Roby said he hollered, "Minimal!"
"It was hard," he said. "But it's worth it to me that it's going to be told the right way and I'm finally going to be able to put it to rest in the sense that nothing else needs to be said about this.
"Nobody's going to need to know anything else. There will be no more books, no more interviews."