Eric Paddock, the brother of the suspected Las Vegas gunman, says his family is "shocked, horrified, completely dumfounded."

Eric Paddock stood in the bright sunlight outside his Florida home, eyes wide and voice straining. “We’re trying to understand what’s wrong, what happened,” he said.

Paddock told reporters gathered on his property on Monday morning that his family had been awakened by a pre-dawn phone call from Las Vegas police. That was how they learned that his brother, Stephen Paddock, had committed the deadliest mass shooting in modern U.S. history.

And now there they were, the newest members of the sad fraternity on the fringe of every mass shooting to dominate a news cycle. Another family left to account for the actions of a loved-one-turned-murderer, grappling with a loss compounded by guilt and betrayal.

Some shooters’ families cope by withdrawing completely, curtains drawn, phone calls unanswered. Others — like Peter Lanza, father of Adam Lanza, who in 2012 killed 20 children and six adults at Sandy Hook Elementary in Newtown, Conn. — take years to publicly express their pain and penance. Rarely do relatives do what Eric Paddock did and immediately try to speak, even if they don’t yet have the words.

In the footage aired by multiple networks, he kept shaking his head, sweeping his hands through the air, as if reaching for something beyond his grasp. He stuttered. "I'm. . . the fact that my brother did this, is . . ." He raised his fist to his temple, then thrust his fingers open, as if to say, mind blown.

“There’s no — there’s nothing,” he said finally. “There’s not even anything I can say.”

For the family of a mass shooter, there are no candlelight vigils, no outpouring of solidarity and strength from their surrounding community. There are only questions, all of them tinged with the underlying implication of blame: What did you do? What didn't you do? What should you have done?

Was there any history of troublesome behavior? the reporters asked.

"He doesn't even have parking tickets," Paddock said.

What about mental illness?

“Absolutely not,” Paddock said. “As far as I know.”

Aradhana Bela Sood, professor of psychiatry and pediatrics at Virginia Commonwealth University, has a name for the isolation and shame experienced by a mass shooter’s family: “disenfranchised grief.” These people, too, have lost someone — whether alive or dead, the family member they thought they knew is gone — “but they can’t really acknowledge it,” Sood said. “The usual psychological events that help us process things, by talking, by venting, are missing for them in these situations. They can’t turn to their usual sources of comfort and solace.”

“We are completely dumbfounded,” Eric Paddock, left, told reporters outside his home. (John Raoux/AP)

Months after the deadly rampage at Virginia Tech in 2007, Sood spent three hours talking with the parents and sister of Seung Hui Cho, the 23-year-old gunman who fatally shot 32 people before killing himself. The family had shied away from the media but granted the interview to a review panel appointed by the Virginia governor after the shooting.

“It was a surreal experience, watching the grief of a family coming apart,” Sood told The Washington Post. “They had learned that they were the parents of this evil character who murdered that many people in cold blood. They carried such guilt, and you could see it. It’s as if their life had stopped.”

They were undone by their shame, she said, shut off from their community in America and from their family overseas. A great aunt in South Korea commented publicly that it wouldn’t be wise for Cho’s parents to flee to their native country.

"We wouldn't let them return," she told Time magazine, "and would even try and block them if they tried."

Even exes find themselves marked by their shared history with a shooter, called to account for the actions of the person they’re no longer affiliated with. Like Sitora Yusufiy, the ex-wife of Omar Mateen, the shooter in the mass killing at the Pulse nightclub in Orlando. Yusufiy spoke of the violence and abuse she’d endured at the hands of her former husband, and her horror at learning what he’d done.

Or Paige Mann, the ex-stepmother of Charleston church shooter Dylann Roof, who had divorced Roof's father years before but told the Daily Mail that the family was "ashamed and embarrassed."

Ex-spouses, siblings, aunts, cousins — all might be asked for some clue or explanation. But the greatest scrutiny is often reserved for the parents of a killer, even if they have no clear answers to give.

Cathleen Alexis, center, mother of Navy Yard shooter Aaron Alexis, answers questions from her Brooklyn doorway in 2013. (Anthony DelMundo/New York Daily News)

When Cathleen Alexis recorded a statement days after her son, Aaron Alexis, killed 12 people in a 2013 rampage at the Washington Navy Yard, her anguished voice trembled.

“His actions have had a profound and everlasting effect on the families of the victims,” she said. “I don’t know why he did what he did, and I’ll never be able to ask him why. Aaron is now in a place where he can no longer do harm to anyone, and for that I am glad.”

Peter Lanza told the New Yorker that he'd spent years agonizing over what he could have done differently, how he might have been more involved in the deteriorating life of his estranged son.

“Any variation on what I did and how my relationship was had to be good, because no outcome could be worse,” he said. “How much do I beat up on myself about the fact that he’s my son? A lot.”

Arlene Holmes wrote of her lingering doubts in an essay published five years after her son, James Holmes, fatally shot 12 people in a darkened movie theater in Aurora, Colo. He was later diagnosed with schizophrenia.

“I have since learned hard lessons, haunted by the idea that the shooting could have been prevented if only I had educated myself so I could have recognized symptoms and taken my son for diagnostics and treatment,” she wrote.

After the violence in Las Vegas, Sood watched the media once again search for explanations — seizing, for example, on the revelation that Paddock’s father had been a convicted bank robber. She is unconvinced of a correlation between the actions of father and son, she said.

“We all try to understand why something like this could happen to a human brain, and we hold on to the feeling of ‘not me, this can’t be me, this can’t be anyone that I know,’ ” she said. “But the truth is that it’s very hard to predict who is going to do what.”

Ten years later, she still mulls the experience of sitting all those hours with the Cho family.

“I felt, as a person interviewing them, both empathy and also thinking, ‘God, never let such a thing visit anyone in their life,’” she said. “Because how do you come out whole? You can’t.”