How can you protect your children from possibly being murdered by your nanny? The answer is to do a thorough background check.

Of history.

The horrific crime that appalled the country last week – two children stabbed to death on New York’s Upper West Side by their nanny – just doesn’t have a precedent I can find. The accused killer, Yoselyn Ortega, is not one of a long line of psychotic nannies. She’s not part of an escalating nanny crime wave. And she seemed pretty normal, if depressed, right up until the afternoon of the murder and attempted suicide. So if there’s a word for this crime it is this: Unpredictable.

Is there any way to prepare for (and avoid) an extremely awful but unpredictable event? Well, let’s consider the case of 14-year-old Gerrit Blank. Gerrit, who lives in Germany, was on his way to school three years ago when he saw a “ball of light” that looked like it was heading straight toward him. In fact, it sure was, and a moment later it struck him.

A meteor. Red hot and pea-sized, it grazed his hand and landed on the pavement with such force that it created a foot-wide crater.

Now THAT was a random event. Amazingly, Gerrit survived with just a three inch scar on his hand (and quite an opening line, if he ever needs one). But what if other parents reacted to his terrifying experience with the kind of fear that has swept New York in the wake of the knife-wielding nanny? Parents today are vowing to buy nanny cams or even never go back to work because the so-called risk just isn’t worth it. “I was starting to feel comfortable with the idea of nannies….But this just puts the pit back in my stomach,” wrote one mom on a parenting blog. “I can’t stop thinking about it.”

Okay. Now say, instead of the slashing, she just couldn’t stop thinking about Gerrit’s fate instead: She doesn’t want her child to get hurt by a meteor. This mom could make sure that her child never goes outside, because of course, he could get hit. And she could re-inforce the roof of her home — a lot — because in 1954 a meteor plunged into an Alabama living room and hit a woman napping on the couch. Another one hit the house of a California pastor just last week. Maybe she’d also wrap her son in some kind of Teflon suit, just in case the meteor came through a window. And at night, when he took his suit off to go to bed, she could go stand on the lawn with a ray gun ready to pulverize any meteor streaking through the sky.

Thanks to all these protections, her boy would be perfectly safe from this random horror…but so would all the other kids whose parents never took any of those precautions. Because the “risk” was infinitesimally small.

So that’s how to avoid having your child murdered by your nanny. You can either organize your life around the idea that your child is in mortal danger, all the time, from everyone except you. Or you can accept the fact that random, terrible events do sometimes happen, but there is no way to predict them and hence no way to prevent them, and rejoice that your child is far, far, FAR more likely to be fine than stabbed.

In other words, you could weep for the parents of the murdered children and then do them the kindness of NOT assuming there was any way a better or more careful parent could have avoided this fate.

In fact, that’s why it is called fate and not “bad parenting come-uppance.”

Lenore Skenazy, a contributing editor of The New York Sun, is a public speaker and founder of the book and blog Free-Range Kids. Her show “World’s Worst Mom” airs on Discovery/TLC International.