We'll never know the reason why a near-genius 20-year-old would invade an elementary school with an assault rifle and slaughter 20 innocent children and several adults.

"He was smart," a friend said of killer Adam Lanza. "He was like one of these real brainiac computer kind of kids."

Shockingly, the so-called smart kid began his spree by shooting his mother in the face several times. But we'll never really know why the disturbed young man of small-town Connecticut was so evil.

And the same goes for Charles Roberts. He was the friendly neighborhood milkman in Lancaster County, Pennsylvania, who barged into an Amish one-room schoolhouse in 2006 and shot ten angelic little girls before taking his own life.

"These children were trusting," said a devastated Amish mother. "They were never even exposed to television, so they knew nothing about this kind of thing."

These sickening mass murders stunned the nation and sent experts scurrying to figure out what happened.

But the theories never quite add up. And they'll never suffice.

That's because no rational explanation can account for behavior that is completely irrational.

We've been down this road so many times.

Late author Truman Capote tried to look into a killer's mind when he wrote his largely nonfiction novel "In Cold Blood." In it, he told of the brutal 1959 Kansas home invasion by two drifters. A farm family was bound, gagged and then shot at close range. Capote speculated about the killers' motivation.

He suggested that a "temporary brain explosion" could result in someone committing "unpremeditated murder."

But then, as now, the explanations just don't cut it. They're more like excuses.

We did learn one lesson, though.

We learned that average, everyday people can be psychopaths.

People who seem to fit into an all-American Norman Rockwell portrait can actually be a page from Alfred Hitchcock.

Evil can have a familiar, friendly face.

What appears normal on the outside is sometimes horribly abnormal inside. There are some, thankfully a minority, so perverted, crazed or angry that they believe killing little kids will somehow ease the pressures of a tormented soul. And that's frightening beyond words.

The sad truth is that no culture, no religion and no grade school is safe from barbarism that punctuates our semi-civilized society.

It's been that way all along, whether we want to admit it or not.

Man's inhumanity to his fellow man has been around since the beginning. The world, historically, has been home to freelance psychos who've done unspeakable things for reasons that defy common sense. From the Christian Crusades to Hitler's Holocaust, no person during any era has been safe, nor will be safe, from evil lurking inside the mind of the misguided and the criminally insane.

Maybe the cause is genetic.

If goodness is intrinsic to design, then so is evil. Moral deficiencies are part of the human condition, and so is mental illness. They're probably inherited the same way we inherit eye color.

Still, I wish we knew the solution. I wish we knew how to put a stop to madness that appears to be inherent, and is possibly growing worse.

And right now, I wish we knew how to ease the pain of grieving families, because words are insufficient.

All we can do is support each other and hope. Many will pray that it never happens again.

But we're only fooling ourselves.

In the end, there's precious little we can do to prevent it.

We can condemn violence and outlaw guns. But it still won't disarm evil.

Truman Capote knew it. "In Cold Blood" told us: "As long as you live, there's always something waiting; and even if it's bad, and you know it's bad, what can you do? You can't stop living."

And so with heavy hearts we journey on, taking measured steps forward in a place ever more threatening than the uncertain world we left behind.