(CNN)The man who stood before me seemed as bewildered by what he had just done as I was.
He had a pudgy face with a squashed nose that looked like it had been broken; sleepy eyes that constantly looked away. A bloody gash on one of his massive forearms had just been bandaged.
His name was Bill Gulley and he was about to pull me into one of the strangest stories I'd ever heard. I was a novice reporter at the time and had been dispatched one muggy Sunday morning to interview him in front of an Atlanta hospital.
Gulley had somehow saved the lives of two strangers in three days. He was a painter who had risked his life to save a co-worker who had suffered an electrical shock at a job site. Then, while visiting the co-worker in the hospital with a bouquet of flowers, he risked his life to save a mental patient who had tried to jump out of a 10th floor window.
People were calling Gulley a "guardian angel." I caught up with him just as he was leaving the hospital after saving the patient's life and asked him how it felt to be a hero.
"I gotta get out of town," he told me. "I'm confused. This is too much."
Gulley's cryptic comment stayed with me for years. Only later would I learn why. A detective called and told me Gulley was suspected of multiple killings. He had been convicted and sentenced to death for murdering an 81-year-old woman and raping her 60-year-old daughter. The detective told me he was considered responsible for other deaths, although he was never charged in those killings.
After I ended the call with the detective, a question lingered: How can someone be one person in public and a monster in private? How can he be both?
Many of us have been asking ourselves that question as we digest the extraordinary news of recent weeks. We've been hit with one story after another of people who appeared to be one thing in public but something totally different in private.
Bill Cosby, the jovial comedian who gave us Fat Albert and Dr. Huxtable, was convicted of drugging and sexually assaulting a woman. The next day, an elderly California man who was a former policeman was arrested for a string of rapes and murders as the "Golden State Killer."
And just this week, New York Attorney General Eric Schneiderman resigned after The New Yorker published an account by four women who accused him of abusing and assaulting them. Schneiderman was a vocal supporter of the #MeToo movement and had helped write a brochure giving legal advice to domestic violence victims.
Schneiderman tweeted a statement saying, "In the privacy of intimate relationships, I have engaged in role-playing and other consensual sexual activity. I have not assaulted anyone. I have never engaged in non-consensual sex, which is a line I would not cross."
Each of these stories has been pored over in detail, but together they point to what former FBI profiler Joe Navarro calls "the big question:"
"Do we really know someone?"
Public lies vs. private truths
Those stories suggest maybe we don't. The easy answer is to accuse these people of being "hypocrites," "narcissists" or even "monsters."
And for some people, Navarro says, those words fit.
Navarro, who spent years studying human behavior and criminals and is the author of "Dangerous Personalities," says about 1% of the population could be classified as psychopaths, and about 4% have anti-social tendencies.
"These are individuals who, with varying degrees, have little regard for others," Navarro says. "Some of them can mask very well just how bad they are. Many of them, because they're not introspective, don't analyze themselves, so they don't see themselves as being evil. They see themselves as being entitled."
Yet the ability to live starkly different lives in public versus private may not be so unusual. Nice people do it, too.
When the folksy journalist Charles Kuralt died in 1997, he left his fans with a similar question: How can he be both?
Kuralt was the pudgy, rumpled journalist who once toured America in a motor home, giving us charming stories of virtuous people for his "On The Road" segment for CBS Evening News. He was like your trusted uncle, the one you went to for sage advice.
But there was a huge disconnect between his public and private lives. He had two families. After his death, his widow discovered he'd had a mistress for nearly 30 years and was a father to her children from a previous marriage. He paid the other woman large sums of money as well as her children's college costs.
Kuralt lived a big lie, but many humans learn to lie when they're young, Navarro says. They have to.
"We humans evolved to conceal certain things, so for the sake of social harmony we cannot be honest," he says.
"Think of children. When they're young, they're very honest. They'll say, 'I don't like her.' But there comes a point where parents talk to us and say, 'Don't say that.' We begin to lie. You really can't go up to somebody and say, 'You have an ugly child.' Society prevents us from this type of honesty."
One of the lies people may tell each other is that someone is all bad or all good. This is something former NBC journalist Linda Vester wrote about in her recent opinion piece published by the Washington Post, disclosing why she accused NBC anchor Tom Brokaw of sexual misconduct.
Brokaw strenuously denied her accusations, and scores of former NBC employees, many of them women, released a letter defending Brokaw, saying how he had treated them with respect.
"Not all harassers are cartoonish bogeymen who mistreat every woman in their path. It isn't really relevant that while a man might have harassed some women, he didn't harass all women. Many men who harass have been well-liked and respected inside the organization and publicly. They are, like all of us, multidimensional."
How to spot a monster
And yet there is a dimension to some people that seems inscrutable. They are predators. They have to hide their private selves.
Some do it by taking on a public mask that's completely different from their private self.
John Wayne Gacy, a notorious serial killer who sexually assaulted and murdered 33 boys and young men, dressed as "Pogo the Clown" at many charity events and children's parties. Some of his neighbors thought he was easygoing and charming. Ted Bundy, who murdered at least 36 women, once worked at a suicide hotline.
Is there any way to tell if you're in the presence of such a predator?
Trust your instincts, some say.
When I met Gulley, the "guardian angel," my instincts told me something was off. Part of it was his refusal to make eye contact. He didn't look like a man who was proud to save lives. His face was impassive, hard to read.
But it was his comment -- "I'm confused.... I gotta' get out of town" -- that lodged in my memory for years. Fugitives say they need to get out of town because they're running from something. Not guardian angels.
My subconscious knew something was wrong before my mind could figure it out. I remember feeling a sense of uneasiness around him.
This is typical, says Gavin de Becker, author of "The Gift of Fear." He says each person has an "internal guardian" that warns them when they're in the presence of danger.
When he's interviewed victims of violence, they usually say they didn't see it coming. But after thinking about their attacks in retrospect, their internal guardians speak.
"If I wait a moment, here comes the information: 'I felt uneasy when I first met that guy,' or 'Now that I think of it, it was suspicious when he approached me,' or 'I realize now I had seen that car earlier in the day.'"
That intuition is a gift from our ancestors; it's part of the limbic system of the brain that warns of danger, says Navarro, the former FBI profiler. He says the subconscious part of the brain processes information that deals with threats and works faster than the conscious mind can keep up.
Some people in other settings or parts of the world learn to listen to their inner voice, he says. It's why those who live in the jungle pay attention to everything in their environment, including their hunches.
"The kind of questions someone might ask who lives in the jungle is, 'How many birds are out? Why are birds chirping on just one side of the forest? Is there a snake on that side of the jungle?'"
Yet many people today are not conditioned to pay attention because they're distracted by their smartphones and headphones. Predators find them easy victims because they don't pay attention to their surroundings or the people they encounter because they're too distracted, he says.
Some people get distracted by something else -- nice people. Cosby, Navarro pointed out, was a professional actor. He knew how to assume a nice-guy persona. So do others.
"Niceness is not goodness. Anybody can be nice. That doesn't mean you're good," Navarro says.
When asked what makes some predators click, Navarro says part of it is their attitude.
"They have a more nefarious form of entitlement," he says. "They think, 'I am so much better than you, and you must be lower than me. You must be submissive to me. You are not entitled to the same things as me.'"
As to why some have this perverse sense of entitlement, Navarro says:
"Nobody really knows."
An imagined reunion
I sure don't. I once thought of arranging a reunion with Gulley, the guardian angel-turned-killer, just to see what made him click. Maybe, I thought, it could be a good story. My first piece about him had already saved his life.
I discovered years later that my article on Gulley's heroics had prevented him from being put to death. His death sentence was thrown out after a court ruled his lawyers should have told jurors about the lives he'd saved, which they'd learned about from my story.
For years, I kept a mug shot of Gulley in my desk drawer at work. In his prison photo, he's not looking at the camera directly. He has that sleepy, faraway look I remember.
If we did meet again, I knew what I wanted to ask: Did he feel any shame? How could he explain himself? How could he be one thing in public and something monstrous in private? How could he be both?
Perhaps these are some of the same questions those who once looked up to a Cosby would ask. I never pursued a reunion with Gulley; a stray comment from a minister I respected dissuaded me. He said the answers to my questions could be too dark. They could dash people's sense of community, their optimism about human nature.
But every so often, when I hear about a Cosby or another double life being exposed, I think about meeting Gulley again.
And then I consider that maybe he would still be confused. Maybe the answer he would give me would be almost as chilling as what he did.
I'd ask him why, and I can see him simply looking away with those sleepy eyes that resist any scrutiny and I imagine him saying:
"I don't know."